I have a d16z6 rebuild bottom with A6 pistons, z6 head with new valve seals, seated valves. Ecu is a virgin p28. I turn the car on it starts no problem. It goes straight to 1500rpm i let it sit and it drops to 100-400rpm and stays on!! Lol ive never seen this before. Did vacuum leak test came out with nothing. Took off the map sensor the car dies down but is still on. If i hit the gas sometimes it jumps to 2000 and will stay there. And ill have to pull the pedal back. I adjust the cable to where it idles perfectly at 1000 and it runs fine for a while. I hit the gas and it slumps back down to 100-300 rpm. Im lost. Someone said its my cable but the cable worked fine for the last motor that was in it. Help me out thanks

 

I like this post very much. I seems too much informative. I like it.

 

Any CEL codes?

Make sure that the throttle cable has a bit of slack. Otherwise, you'll go from a low idel problem to a high idle problem.

Clean the IACV and then adjust the idle speed as per service manual.

 

Ok so new motor. Now im running a d16y7. And guess what i still have this idle issue and when i drive it lags real bad. Completly undrivable. Feels like throttle response. Thing is i drove the engine before i pulled it and was perfect. Only thing i reused from my z6 is the intake manifold. Im running a p06 with no CEL and iacv has been changed three times not that lol