I just purchased my first LT1 car. Its a 94 Z28, which I got for a song. It had an unknown coolant leak, a bad misfire, and a ses light. I fixed a bad heater hose to stop the coolant, at which time I noticed the coolant temp sensor was busted and the plug was missing from the wire. After a new sensor and pigtail, the car runs a lot better and the ses light is gone. It starts and runs fine, but has a noticable miss at idle. I can gradually rev the engine and it will take rpm, but you can feel the miss. If I crack the throttle around 2000rpms, it will take revs... albeit rough. If I crack rd he throttle hard off idle, it stumbles and I get a bad spark knock. Should I assume the coolant leak ruined the opti, or assume that running in open loop fouled the plugs? Will be q nice car once I figure this out.

 

If you haven't changed the plugs and wires yet, I would check them out next and see what you got.

 

I'm really starting to suspect the Opti. It got hosed when the heater hose ruptured. Since I replaced the CTS, the car starts and idles great when cold, but backfires and misfires really bad when it warms up.

 

It should be scanned, as there are some things that don't turn the SES on.

 

I would think if was the opti it would do this at all times ? since it does it best at operating temperature I would look at the I.C.M ???
replacing the plugs and wires are a pain in the a** but if you plain on replacing the opti
you should replace the plugs and wires just to eliminate that being the issue "I.M.O"

 

The more I run the car, the better it is at idle. That would make me think plugs, except for the fact that it acts so bad once it warms up. I suppose I'm just going to have to start at the plugs and work my way back through the ignition system. Will low fuel pressure get a lean backfire in these engines?

 

It was a bad ICM

 

Thanks for posting what fixed you problem !!!
CamaroZ28.com has been a great learning experience for me