I am experiencing a bad misfire in my 1997 Cavalier 2.2L until the engine is up to operating temperature. A few weeks ago I discovered a very bad cold idle but new plugs fixed it and the car ran fine until sunday morning. It starts fine and idles fine for a few seconds then as the idle comes down it starts misfiring and doesnt stop until a few miles of driving. I put in a new IAC and ECT over the winter. What do you guys think of this? What would cause a bad cold idle and misfire that goes away completely when the engine is warmed up? Thanks for any advice/info.

 

A shot in the dark, check compression?

 

Dirty fuel injectors? Since the plugs helped, maybe the fuel/air is off. Try running some cleaner through the fuel system and check how dirty the throttle body is. I like Lucas and use it at least once a year. Also, try resetting your ECU by disconnecting the battery for half an hour, it may be setting some of the cold parameters wrong.

 

Ok an update: I replaced the plug wires and the bad miss went away. I didnt replace the plug wires sooner because they arent that old. Anyway the car starts and runs fine but idles low and will sometimes shut off when I come to stops unless I "2 foot it". This makes me think a problem with IAC but I replaced that a few weeks ago. One thing I noticed was that the new IAC was the bulkier black plastic valve type instead of the stock pointy metal type it originally had. Could this be an issue?

 

If the IAC fit, it is probably the right one. You can rotate it slightly after loosening the bolts, maybe that would raise the idle. You can check the intake manifold for black build-up in the idle air-way. A clean idle air passageway might fix it. Good Luck!