Random misfire
 

I bought a 2002 monte Carlo with 23000 actual miles. it has been sitting for ten years. I am getting random cylinder misfire. I have changed plugs, wires,.air filter, fuel filter flushed gas tank and still same thing. Any ideas would be appreciated.

I'd look into it possibly being the coil packs. On my old Monte Carlo the terminals began to corrode and threw the random cylinder misfire code. After I pulled the wires off the coils I could see the corrosion. Chances are if you see corrosion that's a problem.

Do you have access to a scan tool that can tell you which cylinders are misfiring? Sometimes it will give codes for them and other times you need to watch the misfire data. A misfire can be:
- Injectors
- Coils
- Wires
- ICM
- Plugs
- Vacuum leak
- Fuel or air delivery problems

If you can get a list of which cylinders are misfiring, it will help narrow down to problem and odds are you can do some testing before you toss parts at the problem. Such as if two cylinders are misfiring and they are related to the same coil, swap the coil with another one. See if the problem follows the coil.

Random misfire
 

No my scanner only tells random misfire. I am going to the junk yard and pick me up a coil pack and a icm. The car sat for almost 9 years.

I changed coils and same problem. I found this in back seat but don't know if it goes on monte. I have looked everywhere.
https://cimg0.ibsrv.net/gimg/monteca...65b080e309.jpg

Make sure the spark plug wires are in the correct firing order.

I checked firing order and its correct. Same miss before tuning it up.

How much fuel pressure does it have?

Any vacuum leaks?

Found one in the MAF sensor tube going to intake

Bad Wires
 

I spent some time on this, turns out the AC Delco wires I bought from a local auto parts store had micro cracks in them (maybe they were old). I didnt think this was the problem because I had replaced them. But in retrospect, I got them at 200k miles because I had oem plugs and wires and it seemed like they were do and the problem didnt exist before. The bad wires damaged coil packs. I finally figured out what was going on when I saw arcing on the coil at night. I wrapped electrical tape around the arcing wire were it went on the coil. This changed the random misfire to a single cylinder misfire. I bought 2 junk yard wires for $2 and replaced the taped wire and one still misfiring. This improved things a lot but I still had some less frequent misfiring. I replaced the new coil (I bought thinking it would fix the missfire) with an old one that came off a different cylinder set. And problem gone. Drove it a few thousand miles and then went with the brand wires I found at the junkyard because they looked like much better quality and were actually cheaper then ac delco. NAPA brand "Belden". Haven't had a misfire since the coil swap. I wont go near ac delco again.