missing/rough running

[Z06scentair]

Originally Posted by 8cam

A little more clarity and I think I'm homing in on it. Engine not throwing any codes at all, and vacuum holds 20" for several minutes, pump is cycling like it should. Cruise also verified working perfectly, even though that plunger still doesn't affect the idle.

So I disconnected the IAC and started pulling plug wires. When I got to #4 there was no change in the idle and it's the only one that didn't arc/spark as I pulled it. So I pulled that plug and I swear it wasn't tight. The plug looked very good, no residue, and when I reinstalled it the idle was immediately better. I actually thought I had fixed it, but a quick test drive and it's still missing badly. I ran out of daylight, but tomorrow I'll pull all the plugs and just make sure they are all seated/torqued properly. Then it looks like I have something to figure out with #4.

Make sure the spark is not tracking on the plugs. That's what it sounds like to me. Add Di-electric grease to each plug boot.

Have the injectors been changed in this car? Someone above mentioned that but you never state if they have been changed or not.

If not that is something you should plan for sooner than later. While your under the plenum go ahead and replace the coil packs. Total cost of parts should be around 1k for SS new injectors, coils, and gaskets.