I have a 91 z28 305 tpi auto. ihave replaced all the sensors fuel pressure regulator, fuel pump fuel filter wired my fans direct to key power new plug wires and plugs cap and rotor coil 160 themostat. the car runs good but will start missing for no reason you put it to the floor and it will clear up. i have no check engine lite on. help!!!!!!!!!!!!!!!!!!!!!!!!!1

Similar problem and age car to mine only I have a 5.7. Check electrical resistance of your injectors. Commonly 16 ohms but manual says 10 or more is okay. But at your car age the injectors are prone to fail electrically. I had a couple that were 5 ohms and were too low for the ECM to make correct fuel adjustments. Replaced them all and it now runs great. Another thing that can effect the running is EGR valve at that age. Delphi part number EG10109.
$70 dollars at Napa. Delphi original equipment replacement for the GM 17090107 negative backpressure EGR valve.

Check with John and fuelinjectorconnection.com for injectors. Replaced my 22# injectors with a flow matched set of 22# Bosch Gen III rebuilt units for $170.00. He'll know what injectors you need but this site will tell you if you look around on here. The 305 may be 19# injectors.
3 year warrrenty on injectors.

Keep us posted and good luck

Yeah check your injectors are they below 12 ohms they are bad..

Call Jon up at FIC he will help you, the Bosch III injectors are the best on the market, they have a great spray pattern and flow exactly the same, also they got 3 years warranty, So call him at 770-888-1662

You can lower the fuelpressure to compensate for the larger injectors, but he will help you, call and talk to him Really good service

found it cracked spark plug nothing to do with tpi

Good deal. Glad you found it. Always good to go back over whats already been done just to double check!