94 z28 (100,000) a4
basically my car runs perfect wen its cold but once the car runs for about 30 minutes it starts to misfire and backfire at high rpms, then as it runs longer it gets worse and the backfire/miss happens lower and lower in RPM range until its at idle. I have replaced the ignition coil and module. Opti spark has like 10,000 on it. check engine light throws for a few seconds then goes off. when it was scanned it came up as 34 ets grounded or something...the problem must be heat sensitive...possible its the ecm?

 

34 is the MAP sensor. Check the connector. The clip on the harness is usually broke.

Have you ever replaced the O2s? They are considered tune up items you know?

 

sorry its code 42 which is the ignition circuit. replaced soleniod and coil. new ecm. still no luck. anyone?

 

Never saw a ECM from a 94 defective.

A 42 is shorted to ground.

Did you ohm the white wire from the ICM to the PCM with at least one end disconnected while ohming it??????????

 

It's possible that you have a bad plug wire or burned through. I had the same symtoms your describing. Everything is sooo tight in there it's easy to burn through the wires.

 

Get the logic diagram from the factory manual for diagnosing DTC 42. It will walk you through all the possibilities.