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6.3

Rough idle on your 6.3
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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)
Thank you!

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.
Can anyone comment on how to adjust the butterfly valve?
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?
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.







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 .
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
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
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?
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
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
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?


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
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
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
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 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
That sounds spot on to me!

jim
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?)
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