I have a 94 Z28. My problem is when the car is cold it runs like a raped ape. However once the car warms up and i try to accelerate it spits and knocks and loses power until the rpms get above 3000 rpm's then it takes off like a champ. I just cant figure out whats going on. I replaced the distributor about a year ago and just replaced all plugs and wires. Any help would be greatful.

 

May be related to the O2 sensors, or a problem that causes the O2 sensor to report a "false" lean or rich condition. When the engine is cold, the fuel corrections are limited to what is saved in the long term fuel correction cells in the PCM. Once it warms up, the PCM can use the long term corrections, and the short term corrections, dervived from the O2 sensor data. Faulty sensors or bad readings from the sensors can account of the problem you are seeing.

If you can get scanning software on it, and run a data log of the engine running in both cold and hot conditions, it may be possible to track the problems through the data log.

http://www.ttspowersystems.com/

http://www.andywhittaker.com/

http://www.akmcables.com/

 

I would agree with Shoebox on the O2's since after about 3k RPM you move toward open loop operation. My car did the same thing and it was my O2 connector melted against my collector. I also had a simular problem when I had a cracked spark plug.