PeachParts Mercedes-Benz Forum - View Single Post - All of a sudden reving up and down when cold

Graham · #20 08-28-2009, 12:37 AM

Quote:

Originally Posted by meltedpanda

Ok problem surfaced again

, with no changes in temp or adjustments on my part. SO got out the trusty Ben Wilson publication on How to tune a Bossch FI system
I have read and re read the section on idle . I THINK I understand the procedure as follows - and thought Id see if any of you have done it this way

1) warm up engine to operating temp
2) remove air hose off of AAV , left side I am thinking , but not clear , the one that goes to the throttle plate, and plug - engine idle should remain the same - clearing the AAV as culprit. Or if idle drops replace or clean
3) completely close idle air pass ( adjustment screw) the idle at this point should barely keep car running, if it does not adjust throtle stop screw until lowest possible RPM is achieved to allow it to run
4)readjust the idle air pass to correct idle speed

Now then - I am unclear on the throtle stop screw, is that on the linkage? I am sure on mine that if I screw in the idle screw it will die, so adjusting the throtle linkage may be where I need to place my efforts - what do you all think
despite what Graham said

, I have not removed the AAV and cleaned it , perhaps I shoud start there??

Yes - you should probably clean and test it . You can prove to your self it needs doing by squeezing or plugging the outlet tube from the AAV when the engine is fully warmed up. (I bought a new elbow hose - it is flexible and easy to squeeze). If valve is closed when warm, idle should not change - Mine still changes speed, but not very much.

The stop they are talking about, is on the driver's side of the throttle housing - There is a section in the manual about adjusting the linkages that addresses this. I think it is basically just adjusted so the throttle plate is fully closed when you hit the stop. But I have not read that section for a while.