I've asked this question before but am still contemplating what to do. The car runs great but after heating up it has a very rough idle when stoped and the car is in drive. In reverse or neutral it idles fine. Also it seems to be temperature related. If the outside temp is below 35 degrees it's ok. above 40 degrees and the engin is up to operating temp the problem occurs. Any thoughts or suggestions? Thanks

Does the tach work? Turn up the idle trim. You'll see a box near the brake master cylinder with a numbered dial. Pull up the dial, turn to a higher number and push in the dial. That should raise the idle. If not, disconnect the ELR actuator, the 2-pin connector at the round red thing on the aft end of the IP. Idle should drop or the engine will stall. If no change, either the ELR isn't working or there's no EDS signal to the ELR.

I can't explain the temperature sensitivity or the difference in N or R. One step at a time.

Sixto
87 300D

Sixto
I followed your suggestions. Turned the idle trim EDS from 4 to 7 and the idle went up. Disconnected the two pin ELR and the idle dropped. Put every thing back with the EDS at 6. The outside temp is only 38 degrees so the problem is not showing up. Any other thoughts? Thanks for your help.

EDS and ELR are working. Maybe you cleared a bad connection in the trim box or ELR connection. If the rough idle continues in D but not in N or R, I have to suspect there's a problem in the transmission.

Sixto
87 300D

Just a thought. Could it be the motor or transmission mounts? When the outside temp is warm the rubber on a worn mount might flex more thus causing the vibration. I think the higher idle may also help. The car only has 107K miles and the trans shifts ok.

Could be. Check them. You should be able to get a finger between the 'flats' on the mount and the crossmember.



Only the transmission mount is rubber. The engine mounts are basically fluid.

Sixto
87 300D

I had the same problem... It turned out to be engine mounts for me. Check them, like sixto said, if they start to leak, replace both.

My idles a lot better now after i changed them... you would be sitting and shaking inside the car thats how bad it was lol

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1987 Mercedes Benz 300D Turbo Black/Black