When I start my car the rpms drop to about 400 rpms then without touching gas it climbs to normal. Any ideas what could be causing this?

 

Vacuum leak it, the IAC may be compensating for it thus the slow rise or the IAC just may be dying out and working very slow.

 

I put new IAC on about 2 months ago. I bought it from Advance though since it was already in stock. I find a vacuum gauge and check that out first. Also when I let off the gas the rpms want to hang around 1500 rpms, I put the new IAC and it still does it. Could a manifold leak be causing my problems?

 

A intake leak would make it idle rather high. My bet is your idle air control motor. (IAC) on T-body. Having a non vented airfoil can also cause this. LT1 tbodys get there idle speed via the gap where the after market airfoils are installed. Did you just instal one?

 

No don't have an airfoil. Anyway it was doing this yesterday and day before but today it starts and jumps to around 1200 rpms and comes back down. I don't know what it was but its not doing it now. Also my car used would quickly drop to 800 rpms after starting now it drops to 1000 and when the engine gets to normal operating temp it idles at 800. Could a bad throttle body gasket be causing my problems or would it do the same as manifold leak?