My son has a 1988 firbird 305 TBI. Person that owned the car prior tried to carb it and screwed a bunch of stuff up. I was able to put the original intake, TBI, and distributor back in the car and replace everything he screwed up. Only issue I have now is setting the timing. I know the rotor is pointing to the number 1 cylinder. I had a friend of mine that is a mechanic check it at my house. I can unplug the wire and then set the timing. Once I plug the ECM back in it starts back firing and completely loses the timing I had set. It can only be driven right now with the ECM connector unplugged (runs like crap though). Is this a computer problem? Thing is if you order the computer from Napa, it doesn't come with the prom. You have to reuse our old prom which I don't want to do because what if the problem is in the prom itself? Does the prom have anything to do with the timing itself or is that dealt with by the computer? HELP! I'm about ready to throw a match in this car and watch it burn!
Tony

 

It may just as easily be a problem with the EST system, including the knock sensor. With your '88, I believe the EST should be controlled by a separate module.