I have a 170 and 171. After my f23 manifold swap the idle acted funny. A delayed idle. After the car is under load when in neutral the idle would go to 1000rpm or so and then slowly go down to 700rpm. I have a 170 and 171 CEL that I am either associating with the exhaust or that. I redid the exhaust and the codes still there.
If I focus on the IACV, because it was retrofitted for the swap, just as if one would do a Euro manifold on an F22, what would I look for? Can that cause a lean engine?
This CEL happened a few months after the swap. No vacuum leaks that I can find. No jammed vacuum hoses.

 

if the the iacv is open and the ecu doesn't know (cant compensate) yea, it could cause a lean code. that would be a vacuum leak

 

Ok. That makes sense. I think then there may be an issue with the coolant flowing through the IACV. But if that were the case the ECU would know right? Say there was something keeping the coolant from flowing smoothly through there. Or could the ECU not know? Would that explain a delayed idle?

 

Lean codes are possible due to unmetered air(vac leak), but unlikely to occur on a MAP based system.

 

I asked a mechanic, he said it was possible. But I suppose, the MAP sensor keeps track of the air pressure so a vacuum leak would show. But then again wouldnt the computer see an odd difference in the MAP and Throttle Position and see somethings up?