6.3

Under an old thread, the topic of rough idle came up because so few 6.3s idle smoothly, and they are perfectly capable of it. So, I started working on a list of factors that cause it. Hopefully, this list will live somewhere, like Ron's genious 10 Demandments.

To wit:

Forgot something that I need to add to the list:

Intake manifold gaskets that leak.

So:

1. Worn chain
2. Distributor out of tune
3. Injection pump out of time (timing it is covered on this site)
4. Injection pump out of tune (you need an exhaust gas analyzer)
4. Injection pump needs rebuild
5. Rebuilt injection pump not properly rebuilt (it's happened)
6. Air intake charge heated by coolant circulated through injection throat (should be bypassed)
7. Injection lines not insulated.
8. Obviously, proper plugs and wires in good shape (I've seen it cause trouble)
9. Faulty injectors
10.Leaking intake manifold gaskets

So, tuning issues are potential sources. Hot air and hot fuel are other sources. All of these situations can be very cheaply remedied except rebuilding the pump. While a lot of pumps do need rebuild, the car should be thoroughly and properly diagnosed for all tuning issues before you pull the trigger on this one. You cannot properly tune the injection pump without an exhaust gas analyzer...and your car isn't a true 6.3 until the pump is right.

Best of luck, and please add where appropriate.


Peter in St. Louis
6.3 #1349

Does bypassing the water to throttle body hookups cause any problems with cold starting that are anything to worry about? I would clean up this area in a minute if I thought the benefits outweighed the concerns.

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

Ad:
0.: to much Oil in your IP. Check that oillevel and if necceseaary suck it out.


In the surch for rof idling I would check this item first.

Brad Phillips::: Paul of Europes answer was another potential cause of a rough idle.
I can answer the throttle body hot water line issue. First, I even have the recall notice from Benz about this, the very early 6.3s didn't even have the water line in the throttle body. So, WHY is it there? Evidently, in very cold and wet climates, ice formed in the throttle body. The hot water pipes solved the issue. Recall notice is dated 199 "by memory", so don't take my memory to the bank.
We have removed ours on two 6.3s; seeking maximum horsepower. My theory is that the damn thing needlessly heats up the air, yes, ever so slightly. Did it because I just like to try things out. It worked. We lowered our track time ever so slightly in the year of this last tweek.
I "think" it's a decent idea to remove it. Just make very sure to use stailess steel clamps on your plugs.
This item seems to have zero effect on the idle. It has zero impact on the cold start valves.

P.S. Peter; a very good post. I for one have pulled the trigger way to early on a pump rebuild. Our idle issue, which mimicked vapor lock was the ubber fuel hose from the fuel filter. One additional item to consider is a toasted / shot coil.

On Rob Fultons first 6.3 i disconnected the intake heater because the pipes had corroded out.It does make a difference,especially since you want Cool intake air ,not heated up air .
Unless you live in snow bound USA at the moment ,it won't affect cold start at all.

...There are old cars,and then there are Classics..(Mercedes Benz Ad. 1999)

Thanks for clarification on the hot water to throttle body issue. Here's one back on idle- in neutral, I get about 1000rpm as my normal idle, maybe slightly less. In gear, either forward or reverse, closer to the 600. The car never stalls or does anything strange, actually runs very well. If I'm at a long light, lots of times I'll just put the car in neutral, and that's when it bumps up to about 1000. Is this normal?

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

No that is not normal. The idle should be 560 to 600 rpms at warm idle.

jim

Brad,
Could this be the Idling Throttle Switch not working or out of adjustment? Page 27-23/4 of my service manual.
There was a thread not long ago detailing how this controls the auto when at idle

6.3 #2723, my first classic Benz

Brad, I thought this was an issue in the past. I too, would slip the tranny into nuetral, THINKING it was taking pressure off the engine. It wasn't, better, IT WASN'T. As Al wrote, there is another switch for this, the idle switch. If that switch it toast, the tranny kickdown WILL NOT WORK. Easiest way to tell if that idle throttle switch works? Take it out on a run. Bring it to fourth gear. Now punch it. If it won't kickdown, that switch is toast.
PART NUMBER 0005453404 Ron of Oz found a USA source, about nine months back. I ordered two new switches.

Hi Folks,

I think there is still some confusion on what this "idle" switch does, and to a lesser degree, the kickdown switch.

There is a double-acting solenoid on the transmission. The purpose of the double-acting solenoid is to alter the modulating pressure in the transmission. Changing the pressure changes the shift points, and if the pressure is low enough (idle) then, combined with the lower pressure from the trans oil pump at idle, the transmission will allow the engine to run without driving the output shaft.

The solenoid has three position: normal operation, kickdown, and idle. In normal operation, the solenoid is held in the center position by mechanical springs. The exceptional states are kickdown, and idle. The solenoid has two windings, one in each end. One moves it in the "idle" direction, the other moves it in the "kickdown" direction (the opposite direction). One winding is energized by the kickdown switch, the other by the idle switch. IT IS ASSUMED THAT THE TWO WINDINGS WILL NEVER BE ENERGIZED AT THE SAME TIME. IF THEY ARE, THEN THE FUNCTION CONTROLLED BY THE WINDING WHICH IS ENERGIZED LAST WILL NOT WORK.

If neither switch is broken and both are properly adjusted, IT IS NOT POSSIBLE TO ENERGIZE BOTH WINDINGS AT THE SAME TIME. On the other hand, if either switch is defective or GROSSLY MISADJUSTED, all bets are off.

To expand on what Dan said, only if the idle switch is SHORTED will the kickdown not work (and a shorted idle switch is quite rare). If the idle switch is OPEN, it will not prevent kickdown. (Open is a much more common problem usually related to cars sitting too long.) Note: in the HUGE majority of cases where kickdown doesn't work, it is NOT due to a problem in the idle switch circuit, it is due to a problem in the kickdown circuit or, more likely, with the linkage of the double-acting solenoid.

As it relates to this thread, the idle switch does nothing to effect the engine's idle speed. The idle switch only tells the transmission modulator to reduce the modulating pressure. If the engine's idle speed is too high while in Neutral or Park, the problem has nothing to do with the transmission's electrical system (and, unless there is a vacuum leak in the modulator AND the engine is running too rich, the problem cannot be the transmission in any way).

With an engine idle speed of 1000 rpm, there must be a most annoying jolt as the transmission engages. The fact that the engine speed drops to about 600 rpm when in gear indicates that the hydraulic clutch and transmission are working well. You just need to adjust the idle speed of the engine. You'll also find putting the transmission in gear is no longer an event, but rather just another non-noteworthy task when driving the car.

Chris Johnson
If you aren't constantly IMPRESSED with your car, then it needs fixing.
100.012-12-000790
109.018-12-000019
109.018-12-003834
www.300SE.org

To drop the idle down, do I just turn the adjustment screw on the throttle body? I really don't want to get into adjustments on the injection pump for the obvious reasons!

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

And my transmission kicks down into lower gears no problem- just boot it! [:D]

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

Brad that is the simplest. If you do not have a CO meter,a simple check for leanness is to unsnap the linkage at the throttle body and manually open the throttle alone slowly. The RPMS should increase for a little ways and then fall off. If it dies immediately it is too lean. If the RPMS keep increasing for a long ways then it is too lean. You will need to do this when the car is warmed up

jim

I turned the adjustment screw about two full turns to get it to idle down to about 700rpm, and it looks like right on the money at a little less than that with it in gear and holding with the brake. Seems to be fine on a test drive, pretty smooth at idle now, and definitely not as "stinky" as my three year old son says. I adjusted nothing else, nor tested anything else, just did the turn screw. It's about one full turn from being all the way in, and when I went ahead and did that (slowly) the engine started to shudder like it was going to die, so I just backed off back to the right setting. I do want to see how rich it is running, I believe it is too much so- hopefully this is just an adjustment also...more black wetness inside the intake manifold and throttle body than what I was expecting, but it looks more like excess fuel than a ton of oil blow-by. This would also explain my black puffy exhaust at full throttle acceleration, I guess.

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

Brad, try the disconnected throttle check and that will tell you if it is too rich.

jim

quote:

---

Originally posted by BradPhillips

To drop the idle down, do I just turn the adjustment screw on the throttle body? I really don't want to get into adjustments on the injection pump for the obvious reasons!

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

---

Not the screw with the lock nut,the idle adjustment is a Big slotted screw in the body itself.That screw on the throttle link is never to be touched.If you have ,let us know and i'll explain how to reset your throttle.
High idle is also caused by the distributor advance hanging up.Use a timing light to check the movement of the timing as you rev the engine.It should advance and retard as the revs rise and fall.Disconnect the vacuum and do it again.the results should mirror those.

...There are old cars,and then there are Classics..(Mercedes Benz Ad. 1999)

Hey Ron, I had sent all the fixtures except the butterfly valve on the throttle body for plating, even the small adjustment screw with the lock nut.  I am quite sure I have to adjust it to ensure the butterfly valve stops at the correct position. Can you share with me the adjustment, currently when the car is warm and I press the gas peddle the car tries to die but then picks up the RPM, but definitely dies when I let go the accelerator.  My thinking is the butterfly valve needs to be opened just a tad?

Can anyone comment on how to adjust the butterfly valve?

You have to close the butterfly completly.
Then you take a cigarette-paper and put it between the house and the butterfly.
Now you turn the throttlestop so far, that you just can pull out the cigarette-paper without damage.
Then you fix the throttlestop to that point.

Thank you!

Brad, it is not a good idea to run the car too rich. Excess fuel can end up in the oil and cause premature engine wear. Have you ever checked the oil in the pump?

jim

Will do. I know my way around various carburetors (Webers, Holleys, Motorcrafts...etc.) but this Bosch mechanical FI is new to me, and frankly I'm scared to death of it. I've been reading, and reading, and reading about these cars, and am looking for a good book on tuning the FI. If you have a suggestion, have at it!

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

Hello.

I had problems with setting idle air correctly on both my cars. Last week during transmission swap I discovered same vacuum tube puncture on both cars! It seems to be common problem and it also influences shifting as the hole is on pipe to transmission regulation.
The steel pipe is hitting againts bottom part of inspection hole. I repaired both cars with self-adhesive heat shrink plastic tube and a little bend of the steel tube. Now the idle is stable and transmission is shifting not as random as it was.



See the pipe with heat shrink tube fix.

300SEL 6.3 #1285 (1969 EURO version)
300SEL 6.3 #5346 (1971 US version project)

There is no actual book on the MFI,most info you will find is right here.
Years ago when I first started looking at fuel injection problems ,I was told that if Carb problems come easy,then just think of the fuel injection as being a BIG carburetor which has the same problems but they are spread over the whole engine in the form of leaks,fualty temp sensors,blocked injectors etc etc .
So when looking for cold start problems on a carb,you check the choke mechanism,same thing with fuel injection,check the fuel enrichment and so on.Eventually you learn that certain symptoms are common and can be fixed quickly,( sluggish pick up=governor oil level).

...There are old cars,and then there are Classics..(Mercedes Benz Ad. 1999)

Tried the disconnected throttle test. If I crack the throttle open a bit, the RPM's do increase and then drop off. I can hold the RPM's at the higher RPM by just cracking the throttle open slightly, but if I open it a smidge more they fall off as you describe. In either situation, I'm not opening the throttle very much, no more than a quarter of an inch to half an inch of travel, I'd say, before the RPM's drop off significantly.

1969 300SEL 6.3
1972 280SE 4.5
2007 Honda Civic EX Sedan (hey, I have to offset my fuel bills somehow, right?)

That sounds spot on to me!

jim

It sounds a bit rich to me. "Cracking" the butterfly off its seat should cause a slight increase in RPM, but it has to fall off very quickly after that. At less than an eighth inch the engine should be showing definite signs of struggle.

Chris Johnson
If you aren't constantly IMPRESSED with your car, then it needs fixing.
100.012-12-000790
109.018-12-000019
109.018-12-003834
www.300SE.org

Guys using this topic to solve an idle rpm question. My car on normal operating temp. in Neutral is running at around 700 but when I put it in reverse or Drive the car lurches a little and then the rpm is steady at 550. What do I need to adjust

There cars and then there are BABIES!
1969 Euro Model
10901812000931

It's idling way too fast . Check the ignition timing first,then screw the idle by pass screw in until it's idling at 550 RPM. This will both slow the idling but will enrichen the running mixture.
When you put it into drive, never leave your foot on the pedal until you want to move.
With it in Drive, turn on the air con, turn steering in either direction. If all is well the revs should remain constant. if the revs drop to the point where the engine stalls, turn off the engine and enrichen the mixture on the rear of the pump one click.
Restart the engine, give it a few revs to clear the spark plugs and try the load test again.
You may need to alter the air by pass again,then adjust the mixture yet again. it can become a long drawn out job.
If you put your foot on the brake ,it can alter the air mix ,making the engine run a bit faster.
Make sure the switch on the throttle body is adjusted properly too.

quote:

---

12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section

---

Hi
I have rarely driven my 6.3 in past 2 years. I have upgraded ignition system to ignitor petronix kit and it runs fine, used to hear tires squeaking while shifting.
But the problem that became more obvious now is that the idle rpm drops while shifting from P to D or R and engine tends to stall. It runs smooth, maybe not 100% perfect but far from rough. Tried to increase idle rpm, but the problem happens often, not every time that I shift to D but still pretty annoying when you are in traffic or you just want to park your car and the steering wheel, oil pressure drops as rpm drops and it stalls. I saw earlier in the topic that it may have to do something with kickdown switch...well I wanted to say that it doesn't work perfect neither, takes like half an our before you can use it. Any idea?
Moreover, any instruction for adjusting m100 engine idle rpm? there are number of air intake valves and adjustable linkages, what is the procedure.
Regards

Before you start changing anything I would check the idle switch, and a bunch of other things. Turn on the key, but don't start it, you should hear a click when you move the throttle slightly. You may have to do this from outside the car to hear it. It is the small bakelite switch on the side of the throttle.
It is not quite clear if everything was working perfectly when you last shut it off. If it was and the only thing that changed was letting it set a long time then I would suspect fuel delivery or fouled plugs. Especially if you started it several times when it was sitting, never a good idea. Is the engine oil level particularly high, and does it smell like fuel?
Pull each plug wire one at a time when it is running and see if the idle changes, if it does not and you have spark to it then you have at least one culprit
Have you checked the oil level in the pump? Is there a lot of oil in the valley under the mfi pump?
change the fuel filter, you might also install a clear inline filter between the tank and the pump to see if the fuel is clean, when you do that check the inlet screen in the pump. It is what the inlet hose attaches to, and you may have to take the pump out to get it loose. If you don't, you may tear the rubber mounts.
Check the ignition wires, pull the plugs, look at the cap and rotor closely, also make sure the magnet for the Pertronix is tight on the cam (some times they are loose, if it his check their faq on how the fix with soldering iron or call them), is the magnet letting the rotor seat all the way.
Compression test
valve timing...has the chain stretched beyond five degrees
check valve clearances or lash
check fuel pressure and delivery volume

jim

quote:

---

Originally posted by james lawson

Before you start changing anything I would check the idle switch, and a bunch of other things. Turn on the key, but don't start it, you should hear a click when you move the throttle slightly. You may have to do this from outside the car to hear it. It is the small bakelite switch on the side of the throttle.
It is not quite clear if everything was working perfectly when you last shut it off. If it was and the only thing that changed was letting it set a long time then I would suspect fuel delivery or fouled plugs. Especially if you started it several times when it was sitting, never a good idea. Is the engine oil level particularly high, and does it smell like fuel?
Pull each plug wire one at a time when it is running and see if the idle changes, if it does not and you have spark to it then you have at least one culprit
Have you checked the oil level in the pump? Is there a lot of oil in the valley under the mfi pump?
change the fuel filter, you might also install a clear inline filter between the tank and the pump to see if the fuel is clean, when you do that check the inlet screen in the pump. It is what the inlet hose attaches to, and you may have to take the pump out to get it loose. If you don't, you may tear the rubber mounts.
Check the ignition wires, pull the plugs, look at the cap and rotor closely, also make sure the magnet for the Pertronix is tight on the cam (some times they are loose, if it his check their faq on how the fix with soldering iron or call them), is the magnet letting the rotor seat all the way.
Compression test
valve timing...has the chain stretched beyond five degrees
check valve clearances or lash
check fuel pressure and delivery volume

jim

---

Hi Jim
not sure about idle switch! I should double check tomorrow
Oil level is adequate and doesn't smell like fuel
Pulled wires one by one, idle changes, well not very obvious probably because it is a V8.
Checked the level of oil in pump 2 years ago, but yes there is always oil in the valley under the pump, I drained it 2 years ago.
It is pretty obvious now that engine idle is not smooth and steady, yeah rpm stays at 700, but it's clear that it goes up and down every few seconds.
ignition timing is correct.
I'm really suspicious that ignition is poor under load, maybe original old coil is not enough for pertronix ignitor kit.
And engine stalls right after shifing to D.
So...as I'm sure about timing, plugs, fuel filter, I think we better start from adjusting air/fuel mixture and then switching back to old ignition. So...where to start?

Could very well be a vacuum leak - fuel injectors, throttle body, etc. This can result in an unsteady idle.

Palm Beach Gardens, FL
Niederheimbach, Germany
W109 6.3(6.5)
E55K AMG
CLK63 AMG Gone
Ferrari 400GTC4 Gone
ML400CDI BiTurbo
ML350 CDI BlueTEC
9146GT Gone

The idle is way too high. It should be 550. You need to check things at that rpm. There some tests described above. Have you checked the switch yet?

jim

Unfortunately I have low compression on four cylinders (driver side block), which I assume should be head cylinder or head gasket problem. we did head gasket job for other side 2 years ago, compression on those four are okay, varying form 145 to 160.
So I'll let you know about the rest...so disappointed right now...

Jim, the black switch on throttle body doesn't seem to be active, did what you said, no click. Does it suppose to keep idle at same rpm so while you turn the steering wheel or shift, no significant change occurs?
I doesn't work, what can I do about it?

Here is a reprint of Chris Johnson's helpful post regarding the throttle body switch:

Originally posted by Chris Johnson
This switch is one of two that control the double-acting
solenoid on top of the transmission. The other is the kick down
switch. The switch on the air controller is electrically "closed" when
the air controller is physically closed, indicating that the
throttle is in the "idle" position (even if the engine speed
isn't all the way down to idle). The kick down switch is
electrically "closed" when the throttle pedal is fully actuated,
indicating the demand for maximum acceleration. So, these two
switches indicate the two extremes of throttle position, and when
operating properly, will never both be closed at the same time.
When in the throttle is in the "idle" position the switch on the
air controller causes the double-acting solenoid on top of the
transmission to move to the "idle" position. This moves a rod
attached to the transmission's modulator and causes the downshift
points to move much lower down the rpm range. It also causes the
transmission to dump much of the pressure to the clutch members
so that the transmission is more willing to not cause creep when
the car is at a dead stop and you have your foot on the brake
pedal.

The switch on the air controller can fail in either of two ways.
The first is that it remains closed even after the throttle has
been raised from idle, and the second is that the switch remains
open even when the throttle is in the idle position.
Assuming there is no defect anywhere else in the system, an air
controller switch that stays open when the throttle is at idle
will cause the transmission to down shift at higher than normal
rpms and will be very obvious. Coming up to a stop, you will
notice that the transmission is downshifting prematurely and
raising the engine speed dramatically during each downshift. You
may also notice a greater tendency for the car to want to creep
forward when at at dead stop.

An air controller switch that stays closed even when the throttle
is raised from the idle position can cause the transmission to
slip when accelerating since the transmission is still being told
that the engine is idling. Upshifts can also seem to be occuring
too early too (assuming the transmission isn't slipping so bad
that the car can't build up any speed).

The switch on the air controller is adjustable too, and is rarely
adjusted correctly after all these years. This can cause some of
these fault symptoms to occur, but only at certain throttle
positions, even though the switch itself is perfectly okay.
Personally, I have never seen this switch fail. But I haven't
bought a car in the last 20 years that didn't need the switch

adjusted. There are two hex. socket head screws that attach the
switch to the air controller, and these can be loosened a little
and then the switch rotated by hand. The best way to set this
correctly is with a continuity tester rather than try to listen
for the click of the double-acting solenoid to indicate the
change of state in the switch.

The service book has specific instructions for how to set the
switch, and if everything else is in perfect condition, the
instructions should be followed to the letter. However, nearly
every car has slop in the linkage between the solenoid and the
modulator, and there is frequently a lot of dirt that has built
up on that linkage that interferes with its proper movement (cars
that have sat for a long period at some point during their life
are most prone to this). These things can prevent any operation
of the linkage from making enough noise to hear, can prevent the
linkage from moving through its full range, and can even prevent
the linkage from moving at all.

With the engine off, and using a continuity checker, adjust the
switch on the air controller so that there is continuity through
it when the throttle linkage is resting at "idle", but once the
throttle linkage has been raised from its idle position just the
slightest amount the switch must then go open and show no
continuity. When the throttle linkage is returned to its idle
position the switch must again show continuity.

This sets this switch so it is satisfactorily adjusted. The
biggest reason that these switches become mis-adjusted is changes
in the throttle linkage synchronization. If the idle stop screw
on the air controller is changed in the least, the switch is now
definitely no longer adjusted correctly. Likewise, if either of
the rods in the throttle linkage have been lengthened or
shortened, the adjustyment of the switch should be checked.
A caution: there is no way to adjust this switch to overcome
other problems in the double acting solenoid, its linkage to the
modulator, or the modulator itself. The switch can only be set as
described above, and then other problems can be addressed
separately.

Since we are on the subject, let me also point out the net effect
of wear or limited movement in the double acting solenoid and/or
its linkage will cause the modulating pressure to not drop as low
as it should when the throttle linkage is in the idle position,
and the modulating pressure will not go as high as it should when
in the kick down position. The pressure not dropping as low as it
should at idle may be slightly annoying, but the pressure not
going as high as it should at kick down can actually allow the
clutch members in the transmission to slip, with the eventual
failure of those members if (and when) they get hot enough. This
is one of those things that should be checked periodically, and
certainly should be part of the inspection and sorting out of any
new acquisition.


Palm Beach Gardens, FL
Niederheimbach, Germany
W109 6.3(6.5)
E55K AMG
CLK63 AMG Gone
Ferrari 400GTC4 Gone
ML400CDI BiTurbo
ML350 CDI BlueTEC
9146GT Gone

You have to disconnect the linkage and move the throttle by hand. If it still doesn’t work you will need to back the idle stop screw out ( note its location ) or loosen the two Allen bolts and twist it back and forth. I would loosen the bolts. If still no click then bridge the two wires if still no click then most likely it is the switch.
When the car is idling in gear it is supposed to act like pushing in the clutch.

jim

To add to Jim's Comment, If the switch is faulty or you join the two wires together,the trans will feel like it is slipping .

Thank you everyone, these posts are going to help a lot!
But I have to rebuild the engine! Four broken pistons and rings! At the moment I've sent the cylinder block and heads for machining.