Hey, I got some problems. I have an 89 Iroc that I swapped a L98 out of a 1988 GTA into. It was running fine for the last 1200 miles but now when you start it backfires and misses. It's not every time you start it. It seems to be every second time. The idle is all over the board. 800 to 2500RPM hunting up and down, you can't even drive the car. I went ahead and put in a new GM Distributor Module, distributor, coil, fuel pump, fuel filter and tried another ecm. I have checked the timing and everything is fine. The interesting thing is that if I disconnect the wire to check the timing the car runs fine. No backfiring or missing at all. Now you couldn't leave it like this but at least it will idle and you can move the car around. I'm lost on this one...maybe try the ESC module? The wiring harness could be shot I guess but why would it run fine when I disconnect that timing wire Any help would be great.

z28redline

 

well if you disconnect it thats base timing, which is about 6 degrees, sounds to me like a ect issue of some sort and the ecm is changing the timing incorrectly for some reason

 

Yeah I agree that must be the problem. Just lost as to what would cause it.

z28redline

 

did you swap in the 350 ESC and knock sensor?

They differ from the 305.

 

JB22, I did change the sensor.

Just for the record I found the problem and it turned out to be the new distributor that I just put in was no good right out of the box.

z28redline