chevy power

I bought a car to flip that needed a motor. I got the motor put it in, the motor needed a head gasket, it runs fine now no issues smooth idle, clean fresh head,valves dead on. I am using the throttle body from the old motor which ran fine until it was run out of oil.
I bled the cooling system twice no bubbles in there at all. Problem is I am getting a p1505 and p0505 simultaneously, they are pending codes until you go for a few mile drive then the dash light turns on. These are the only codes showing up. I have cleaned the IACV and checked for vacuum leaks, I have narrowed it down to the IACV. When the car is warm it idles around 1500-2000k, if i put my finger over the port in throttle body it calms down. Before I just jump and buy a new IACV any one have any other experience with these codes?

Thanks guys and sorry to beat these idle issues to death, and don't hate on my name, my daily driver is a 98 civic Ive had for 4 years. Chevy sticker on the honda and honda sticker on the chevy.

lazlong

P0505- Service manual says to replace according to your diagnosis.

P1505- Service manual says to check for vacuum leak at the PCV valve and hose, EVAP canister purge valve, throttle body, and brake booster hose.