Today’s Symptoms:

Idling Problem with 2001 ML320 Mercedes Benz

This idling problem with ML320 Mercedes Benz was first received in a body shop after it was damaged at front left side corner in a collision. The body shop however has a starting problem after the body repairs which was accompanied by a very rough idling , jerking and mil light P0300 (random misfire) after I scanned it. The engine is a V6 or 3.5L and has an automatic transmission.

Diagnostic for idling problem with 2001 ML320 Mercedes Benz:

When diagnosing this type of problem, I start with very basic diagnosis like what are the requirements to run an engine properly like fuel,air,spark,compression and proper timing? When finished with the basics I checked all wires for the injectors, coils and sensors to ecm (engine computer). I found cylinder#1 and #4 primary plugs were broken and after repairing the wires… it seems better but not smoother (The damage to the cylinder #1 and #4 must have happened at the body shop). I rechecked all fuel lines for any pinch wires (OK) and cleaned all the injectors. I also checked the spark plugs but there was no improvement. I reset the code but it came back later after running the engine for sometime.

Fix for idling problem with 2001 ML320 Mercedes Benz:

New code came after I road tested the car again which is p0306 (cylinder #6 misfire). When I reviewed the repairs I did above including testing the crank sensor and timing which were within specifications. I began to narrow it down to #6 cylinder misfiring which I have to double check. Looking closer at cylinder #6 coil, I discovered it was replaced with cylinder #4 coil. The mistake must have happened when I was repairing the primary plug wires. Relocating the coils corrected the problem and the idling problem with 2001 ML320 Mercedes Benz was now running smooth. The fix made sense because the original code was P0300 but changed to P0306 after I repaired the primary plug wires. Hope you will not make the same mistake I did.

Thanks!

Richard