My car has developed an annoying idle surge over the past few months. I recently installed a new long-block and re-used my DPFI intake manifold that was on the original engine.

I am certain the problem lies somewhere in the IACV. After warming up, the idle will surge between 1K - 1.5K. I have tried a different known good ECU, a different IACV, cleaning the IACV screen, a brand new IACV gasket (I was sure this was going to fix it but it didn't), and am about to try a different engine wiring harness.

I can pop the IACV hose off the intake box and put my thumb over it and the car idles beautifully. Engine grounds are good - I made sure of that after putting in the new engine. If I unplug the electrical connector to the IACV, the surge just speeds up. Turn on the A/C and the car stops surging but I have a high idle (around 1.5K). No CEL, but I have gotten one for IACV a few months ago.

Any ideas for things I maybe haven't thought about?

**ETA**

I just read in my PGMFI training manual that I need to ensure there is no continuity between the winding and case of the IACV, and that the winding should have about 11.5 ohm of resistance.

 

I would double check your harness plugs are connected to the right sensor. The air temp sensor, IACV, and the map sensor plugs all look the same. Seen this happen alot.

 

Thanks. I actually made that mistake the last time I had the engine out and learned my lesson then. I'm sure they are in the correct spots now.

 

Just an update for closure - the IACV I used as a replacement had the same problem as the original one. I replaced it with ANOTHER junkyard IACV and now my car idles great.