Before i sent away my pcm i was using a buddies pcm which was tuned for a smaller cam. The car ran ok but when ever it got to normal operating tempature, it would back fire a lot and not hold an idle. If i tried to let it idle, it would die and if i tried to start it again, it would make loud backfires and not start up untill it cooled down. the problem persists after the tune.



thanks

 

Since one of the causes of backfire is running too lean, and when the engine goes into closed loop, after it warms up, it leans the mixture then I would have to say your running too lean.