I have a '91 Z28 with the 5.7L engine with 81K miles on it. When I first start it up and the engine is running "cold" it runs and idles fine. As soon as it warms up to regular running temperture it idles and runs very rough. When I'm at a light it feels like it is ready to stall, and while driving if you let up on the gas and as soon as you give it gas again it bucks...the RPMs drops like a rock then jumps back up. I just had a tune-up done and it still the same. The shop says it shows no error code when it is on the computer. Any suggestions??

 

i would think a code would show up...but it sounds like a problem with a sensor. since it only happens when its in "warmed up mode"...can never remember if that's closed or open loop....

my first thought would be the O2 sensor