Thread: HOW TO: Bad idle troubleshooting

i just found my culprit with it. vacuum leak......

Same here. I have a leak somewhere in the evap system. I pulled the hose coming off of the purge volume control valve and plug it with my finger. The rough idle magically went away.

I think checking for vacuum leaks should be bumped up to the first thing one checks, before going through all of the other things listed in the original post. With some of our cars well over 20 years old now, the original rubber hoses are pretty much at the end of their life.

My idle is really high - around 3k... Can air being in the coolant line that goes to the AICV under the intake cause this?