Did the same thing, dregich89, replaced a motor with the stock one and have the same issue. High idle with the computer screaming IACV. Have to test the voltage to the connector tonight... Let us know what happens

 

Any vacuum leak will cause the engine to idle high. The IACV code is set whenever the ECU can't control the idle for whatever reason, it does not necessarily mean that the valve is the problem.

 

There are two different IACV trouble codes for 6th generation Civics (P0505 and P1508/P1509), whereas 5th generation Civics have only one (code 14).

P1508/P1509 specifically signifies electrical problems in the IACV circuit, whereas P0505 indicates IACV mechanical problems, as well as non-IACV issues such as vacuum or intake air leaks, idle screw misadjustments, and TPS or ECT sensor problems. Therefore, the OP needs to pull the CEL code with an OBDII scan tool in order to help focus the troubleshooting.

 

nah the throttle screw an cable are both fine but i got the code it was P0505

 

1) When the engine is hot, remove the air intake, start the engine and, while it's idling, use your finger to cover the port in the throttle body leading to the IACV. Does the fluctuating idle continue or cease?

2) Cover the top of the throttle body with the palm of your hand while the engine is idling. Are you able to kill the engine?

3) Disconnect the ECT sensor or TPS, start engine, and test whether the idle fluctuation ceases.

4) Describe how you bled the cooling system