I own a 1992 K1500 Blazer with the 5.7 350, while in idle in park,drive and reverse the rpm spikes violently from 1k rpm to 1500.
This is a link to a gif of the issue while running Imgur: The most awesome images on the Internet (foot is completely off the pedals)
I have tried just about everything i can think of listing off being the ECM, MAP, IAC, EGR, replaced all the vacuum lines, New spark plugs and ignition wires. This issued started after i installed a edelbrock TBI intake manifold.
I cant find the issue and after 3 days at my favorite mechanics could not find the issue. The car is still capable of being driven but i have to keep on the throttle to avoid the engine surging too violently and *stalling on itself* its a automatic.
I have no issues while the car is in movement this occurs when at a full stop in park/drive/reverse
If anyone has any ideas or encounters with this issue any information will be extremely helpful.

 

I would start at fuel pump and the TPS (throttle position Sensor)


Good luck

 

could be vacuum line also. Listen for leaks

 

Ive sorta given up on trying it on my own, im bringing it into the chevy dealership in a week or so, My last thoughts are the TPS but ive never messed with one of them and i am tired of buying new parts