Ive got 94 4.0, it started to go to hi idle on start and was slow to return to idle when comming to stop etc. Pulled the electrical connector from the idle air assembly, normal idle at all times now.

Cleaned the valve per the guidence from a parts house, still high idle, pulled the connector again.

Question, what exactly does this do, is it really needed? They want $50 for a replacement but I don't know if its really needed.

Please advise.

TIA

Hank

 

It does just what the name indicates, it provides a higher idle speed when the engine is cold, the AC is on or other load conditions.

 

Since cleaning the MAF, throttle body and IAC plus a PCM reset on my 97 Ranger 4.0L, my idle went from slightly high(1000-1100rpm) to 1400-1500rpm! Of the three things I cleaned, I figured that I may have screwed up the IAC. My cost $111 with my Ford discount. It still idles fast but the IAC is getting a high voltage. It almost suggests a bad PCM. I even tie-wrapped my old IAC onto the engine, drove till it warmed up and plugged in the old one. I get System Too Lean Bank1/2 but still got them during my IAC test. The pinpoint tests for IAC take a little turn if you pop a P1506, IAC OverSpeed Error which I did get only once since my cleaning job. It has you check for a stuck EVAP Purge Valve which routes gas tank vapors back into the throttle body. The purge valve has a duty cycle from 0-100% depnding on speed. I haven't checked the valve out yet.

I can cruise without problems but when I start to slow down my Fuel Trims start going rich, at idle the HO2S stop switching and it goes back into a Open Loop. An Open Loop like it a cold engine starts richening up the mixture, lites up my CATS and the idle gets rough. I was looking at the ECT voltage when I popped back into a Open Loop the other day, so I know that the ECT isn't the problem, although one can't say that the PCM is seeing things correctly. I popped a Ignition Coil Malfuction code too and I have no idea why that came up at all!!

Any testing on my problem limits me to about five minutes or so at warm idle before the above happens!

I made contact through a friend at work with Ford's Racing/High Performance Div. and they are at a loss too but they are more into the old pre OBD-II systems.