Originally Posted by chitown
The idle isn't high, it's pretty normal but just dips down to where you can feel the engine kind of stutter and then go back to normal, and over and over.
The check engine light has been on since summer, it came on when the secondary air pump died. But after getting that replaced, it's still there.
I'm not sure if it's just the cold and windy weather but sometimes it does seem like the car is a bit rough, like it has lost a little bit of its "pickup" but that could just be mental
windsor - yep a bad plug / connector can do it too...
chitown - get a code reader to check why your check engine light is on, or if you have an OBD II e36 you can do the self-diagnostics to check this. It sounds like your oxygen sensor is dead... but here's a way to check if it's a vacuum leak:
1 - put your car in park (or neutral as it may be).
2 - allow your engine to warm up to normal operating temperature.
3 - rev your engine to 5000rpm, hold it there as steady as you can for a full 40+ seconds. (the longer the better)
4 - let go of the gas slowly until it is back to idle speed.
now, is the idle still unstable? if your idle is now fine, then you likely have a vacuum leak, or your MAF plug (as windsor mentioned) can be the culprit, there is also a remote possibility that your air filter is clogged and your car is having difficulty getting the proper air/ fuel mixture, and only after revving up can it suck in enough air to even out.
if the idle is stable at first after doing this, but then it begins to get bad again after driving around for a few minutes---then your MAF is probably dead.
and last, if doing this test makes no difference at all and your engine is still idiling weird, then your oxygen sensor (o2 sensor) is likely dead.
chances are that it is not your ICV, as if your ICV sticks your engine will usually rev up to 3000 rpm, then nearly stall, and go back and forth like this. But my understanding is that your car is not revving this high when at idle though.