94 z-34 problems!!

[Dan94Z34]

I am having problems with my 94 z-34. When I start it before I go to work the engine races up and down. I will rev to about 2500rpm's then go way down to 800 or so. It repeats this a couple of times then stays at about 1000. I do notice when I it done racing the engine seems to have a shudder to it. After the motor is warmed up it runs fine no shutter. I do notice after I put the thing in park, after being warmed up the rpm's will go up to about 1800 or so stay there for 2-3 seconds then come back down to idel. Suggestions?

[White93z34]

could it be the dreaded intake gasket?

[DaveFromColorado]

bad Idle Air Control valve?

[topless94style]

I am with the gasket, but you can check the IAC first would be easier to do.

[GP1138]

I've had 2 IAC valves that suck. Check that first, and DON'T GET A JUNKYARD PART:

 

I've had 2 IAC valves that suck.

 

Yeah, those came from junkyards. They sucked.

[Slade901]

You might want to clean up your IAC and the spot where the IAC goes to the throttle body. It builds up hard carbon and so clean it out good and test it before getting a new one.