W124 rough warm idle, misfiring
 

My 95 E320 has 137K on it - the engine runs fine at startup and for 3-4 minutes of cold driving. Once it warms up, it runs very rough, missing and almost stalling at stop lights, with poor to no acceleration. As long as I feather the gas, it goes, but anything more than a light touch on the gas and it hesitates and occasionally backfires. It seems okay at higher or highway speeds, although I haven't tried any passing manuevers or the like. I replaced the wiring harness recently, have no check engine light, and no problems with ABS, which (I think) eliminates the OVP. So now I'm wondering if it could be throttle actuator, coils, mass airflow sensor?

Any thoughts or observations to help a newbie? Thanks!

Was the rough idle and misfire there before you changed the harness? Mark

Have you checked the distributor cap and ignition wires? I had the same problem with mine, the rough idle and misfiring cleared up after the cracked distributor cap was replaced.

Idle was rough before harness replacement - trying to diagnose the rough idle led to the harness replacement when the wiring crumbled. Another data point - engine ran way smoother, almost perfect, when outside temp was below 35 degrees - the colder the better.

Mechanic replaced the plugs, checked the plug wires and said they were good. One knowledgeable type said that one or more of the coil packs might be bad - is there a way to test that theory without replacing them?

Arthur Dalton's reply to the other "Rough Idle" post is a good start. As SteveBFL has written he replaces these every time he replaces spark plugs on the 104 engines. Mark

The coils were my problem when my 300e with the m104 had an idle problem, so I would echo the above advice.