Lets say I am cruising down a street, and come up to a down hill section. When I put the clutch in the motor's rpm's will come down and go too far down (ie 850) then they will come back up and beyond where they should be (1200) then drop back down. Eventually it has a steady idle.

I only notice it because when it drops down I can see the lights dim a little and the oil pressure goes down from like 30 to like 25 or so. Nothing too bad, but I figure that the computer can do better even with a bigger cam.

So you guys think the IAC motor is just clogged or is completly busted?

Thanks,
James

 

My 847 did that too. Corrected it with adding a ton to the MPH vs IAC table.

 

Mine does the same thing. But mine seems to run good and idle great and then it'll do it for a while then straighten out

 

LT1's are very sensitive, especially SD, due to the way GM made the manifold, when it comes to larger cams. The back of the factory T Body is closed off so the IAC controls the idle, but when we put a aftermarket T Body, it causes the idle to be bad. If you look into the manifold the ports are tiny little holes where the air comes in , and when you have a bigger cam , it causes #1 cylinder, as it is closest, to feel it is low on vaccum, and sometimes causes the car to run rich on that bank, lean on the other, so your ecm is trying to compensate the idle with the IAC.
Tuners can fix this.