Returning to idle speed

[gugel]

My stick shift 230SL runs and idles very well, except that sometimes when I come to a stop when it's warm the engine slows down to only about 1400 rpm until I then goose the accelerator once., whereupon it does return to idle speed.  It doesn't seem to be the dash pot keeping the throttle open slightly -- seems more like a linkage adjustment problem.  However, I've fooled with the linkage a lot without lasting success.  I can get the problem to disappear by carefully adjusting the linkage, but then the next time I actually drive the car it soon comes back.  It's by no means a major problem, but the car runs so well otherwise I'd like to fix it.  

If anybody has any ideas as to just what part of the linkage (or other factor) might be causing this, please let me know.

Thanks,

Chris

[A Dalton]

It is a good idea to change out both the ball ends and the cross shaft bushings if the car has some high miles .
 The cross shaft bushings don't seem to get looked at much, but new ones make a world of difference.
 These MFI units need tight links betwen the throttle plate and the pump, as the geometry is critical to A/F mix throughout all ranges...
 You also want to check all pivots from the pedal through to the engine links..sometimes they just need a little oil/cleaning, specially on the firewall brackets

[Cees Klumper]

Could it be the adjustment of the intake venturi flap (which at idle should be almost binding and against its stop)?

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[A Dalton]

Another possible worth looking into is the advance weight springs/plate in the distributor.  May have a broken spring or advance mechanism problem..not allowing  retard , which would result in high RPMs at idle, even though all pump/throttle links are at zero degrees...

[gugel]

Many thanks for the suggestions.

quote:Originally posted by cees klumper

Could it be the adjustment of the intake venturi flap (which at idle should be almost binding and against its stop)?

It's not that -- the venturi flap is adjusted just the way you say.

quote:Originally posted by A Dalton

Another possible worth looking into is the advance weight springs/plate in the distributor. May have a broken spring or advance mechanism problem..not allowing retard , which would result in high RPMs at idle, even though all pump/throttle links are at zero degrees...

I'm not sure I see how this could cause the symptoms I have, and wouldn't this kind of defect cause other symptoms as well?  Is there any way to check this while the engine is running?

quote:Originally posted by A Dalton

It is a good idea to change out both the ball ends and the cross shaft bushings if the car has some high miles.  The cross shaft bushings don't seem to get looked at much, but new ones make a world of difference. ... You also want to check all pivots from the pedal through to the engine links..sometimes they just need a little oil/cleaning, specially on the firewall brackets

The car actually has low miles, but I have changed the ball ends and cleaned and oiled most of the pivots -- can't remember whether I got the ones on the firewall brackets.  I will check those and the cross shaft bushings.

Chris

[A Dalton]

<<Is there any way to check this while the engine is running?
>>
 Timing light will show erratic advance/retart..
 You can also check it not running by removing the dist cap and hand turn the rotor and see if it snaps back to normal position without any bnding or assistance..
 You may also try the vac diaphragm with a hand vac pump for funtion..
 The whole premis/possibility here is if the dist is not returning to correct position, then you have an advanced ignition , which will raise idle rpms...just something to consider/ check..
 could even have a stuck rack or rack solinoid.
 look aroud , you will find it..
I have even seen bunched up floor mats/rugs cause these problems....

[gugel]

OK, I finally found the problem!!  It was indeed the dash pot, which was cocked slightly -- just enough to make the plunger  bind against the front guide tube sometimes.  I cleaned it up and adjusted the angle, and now it works fine!  The car now even seems to run a little better, as it returns to idle speed more smoothly, as it should.

Thanks again for all the suggestions, which helped inspire me to try various things until I found the culprit.

Chris