My brother gave me an '89 Camaro, 2.8L V6, auto, that he had sitting around for the last year. I tuned it with the standard items (plugs, wires, cap ,rotor, filters, etc.). It needed a new catalytic converter which I had installed with an O2 sensor. It runs fine below 2500 RPM; above that it sputters. It seems to run better while the engine is cold, then will sputter when it gets up to operating temperature. It ran perfectly one morning on the way to work; air temperature was 35 degrees, it ran to 4500-5000 RPM without a problem. Haven't checked any engine codes yet. Any ideas - MAF sensor, throttle position sensor, coil . . .?

Sound like a distributer problem. It could be that the advance springs are stuck or need to be rebuilt. You can try Auto Zone for the engine code, see what that may turn up. If your problem is the timing, just buy a new distributer. Most of the time it is cheaper to do that than rebuild the old one. Also, if the cat is really bad off, it can cause problems "running smooth". That's easy to unbolt and replace yourself. They can run up to 200+ bucks. See if Summit racing has one for your car. Hope this helps.