I just bought a 1995 monte carlo z34 with a 3.4l dohc motor, it has 140k miles. The motor idles real bad when its cold. It will be under 1000rpms and sputter and miss and then the rpms will randomly jump to to like 3k and then back down. The gas pedal is very sensitive during this too. After a few minutes the check engine light comes on. Once it's warm it runs excellent and the check engine light turns off. If I start the car warm it starts with no problems. I'm guessing it could have something to do with a temp sensor or something like that. I am experienced with auto's and can replace anything, just trying to figure out whats wrong before I bring it to a dealer to run a diagnostics check on the motor.

 

check idle air control valve. also may have a vacuum leak. take brake cleaner around the intake and listen for a change in the idle of the engine.

 

check the 02 sensor

 

I have the exact same problem with my '95 Z34.
Wouldn't the O2 sensor be "out of the circuit" because the PCM is in open loop while the engine is cold(first started)?
jogas