I'm working on a 1999 Civic lx standard trans with a D16y7. The car is getting the P0505 code. Checked for vacuum leaks and all is good there. The idle fluctuates from 1000 to 2000 rpm. Idle fluctuation only happens when vehicle is warm. The idle goes back to normal when the fan kicks on and goes back to fluctuating when it kicks off. My question is can this be the ECT sensor causing the idle issue?

 

P0505, IACV manfunction.

Test the IACV, clean it, and if all else fails, replace it. The CEL code points to the IACV, not the ECT.

 

In the one thread about the possible causes for the P0505 code it does list an ECT as a possible cause. I was wondering if the ECT was causing it due to the motor changing idle with the fan turning on and off.

Found here:

https://honda-tech.com/forums/showth...ighlight=p0505

 

Worry about what the code actually means before you worry about tertiary causes.

 

Rule out the IACV first like suggested. Then if the valve is good look closer at the ect.

The three wire IACV on those is on the throttle body

 

Was able to work on the car today. Removed and cleaned the IACV. The CEL is gone but idle is still bouncing. I covered the port on the throttle body and the idle went down the 700. Guessing the IACV will need replacement.

 

It's uncommon for the IACV to go bad.

1) Bleed cooling system.

2) Try to adjust the idle speed -- see diagram in FAQs sticky.

3) Test the TPS and the ECT sensor.

 

Before cleaning the IACV I did unplug the connector on it and idle still did not change at all. That is what is making me lean towards the IACV being bad. I probably won't get to take another look at it until next week and will check the coolant system, etc.

 

Good point. Did the idle still fluctuate with the IACV unplugged?

 

I did the test with the idle fluctuation happening and idle did not change at all. Seems like the valve maybe possibly be stuck open? I covered the port on the throttle body that leads to the IACV and the car idled perfect.

 

Makes sense to me.