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Erratic Idleling When Stopped

I have a 1997 MBZ 320 that up to two months ago was driving fine. I took it in for regular maintenance service back in may and was told that besides regular air filter and fluid changes they had to replace the poly V belt, because it was worn out. A week after that the car started to idle very erratic when I would stop at a light (RPM?s would jump up and down) and the engine and electronic check lights would light up.

I took it back and the mechanic, hooked it up to his computer and determined that he would replace the fuel pump, cam sensor, spark plugs and B lift switch. The car seemed to work fine for a few days and went back to doing the same thing.

Again, when the car is on drive and stopped, the idle ling becomes very erratic with the tachometer meter jumping up and down. If I switch gears to neutral it tends to smooth out somewhat.

Please help me with this. I find myself shifting to neutral at all stop lights.


sounds like you either have a vacuum leak or a bad idle air control valve. the mechanic could have accidentally unplugged a vacuum port somewhere when replacing the belt.

check all of the vacuum lines and connections. the easiest way is to spray a little brake cleaner on the lines and listen for the rpms to change

Check the electrical connector plug to the MAF (Mass Air Flow) sensor. Sometimes, it has to be disconnected in order to remove the air filter. It may not have been reconnected fully.