When my iroc is in park the engine revs up and down. It does it pretty bad. What's causing this ?

 

I would have to say that it i sa vaccum leak some where. Check the hoses to seel if they are cracked or broken.

 

sounds to me like an IAC (idle air control motor) that is either very dirty or just worn out. That is a very common problem, but then again so are flakey MAF's. The MAF problem or even vacuum leaks should set a code eventually, but many times a faulty IAC will never set any code.. the idle just goes up & down, up & down and engine sometimes will die in gear.
On a rare occasion I have seen idle fluctuate like that because the tranny was 2 qts low on fluid (big air pocket in the TC).
Let us know what happens.
good luck


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White 1986 Irocz, 305/383 with Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, 3.25:1 rear, Mcreary Road-Stars, single 3" Borla exhaust, Linginfelter-TPI camshaft pulls 17" vacuum solid. N/A runs 10.9 @124, Crack-runs 10.3 @135... haven't run at track since Oct-99