Multiple IAC FAILURES??? Idling Problems won't go away

[SyberTiger]

I've had idling problems on several occasions. It appeared the problem was a failing IAC. I replaced it with an Advanced Auto BWD made IAC. This seemed to fix my idling problem. Six months later, my idling problem was back. From what I read about aftermarket IACs I decided my BWD part failured. For a quick sanity check I returned the BWD part to swap it for a new BWD part. The idle problem became even worse. So, I dug some more and decided it was the EGR port hole in the throttle body that was plugged up and needed cleaning. You can read about that solution HERE.

Also, as part of my "fix" I returned the BWD IAC part back to Advanced Auto for a refund and I replaced it with an Motorcraft OEM IAC. My idle was restored and everything was wonderful with the world. Fast forward 8 month later and AGAIN I'm having idling problems. So I returned the IAC and got a new Motorcraft IAC. It fixed the problem somewhat but for a couple of weeks then...you guessed it...idle problems reared their ugly head again. So now, I'm thinking I have yet another bad IAC. I return it and now I'm on my third Motorcraft IAC. The newest IAC once again fixes my idle problem. That brings me to today. After two months on my third Motorcraft IAC and 6th IAC (including the original and BWD parts) total I'm having idle problems again.

Just to clarify, my current idle problem is that the when the vehicle is warmed up and the tranny is in PARK or IDLE the engine is idling at around 1800 to 2000 RPM. When you put it in DRIVE or REVERSE obviously it's not a good thing at that RPM and you can feel the car wanting to move forward when at a stop light.

It has become apparent that this is NOT an IAC problem. There is no way my luck is that bad. So, my question to those who have similar IAC problems what else should I be looking for? Is there a control module for the IAC that goes bad? I cleaned the MAF sensor but that really has nothing to do with idling anyway.

 

[2000StreetRod]

fast idle when cold?

If your engine idles faster than normal only when cold then you may have leaking intake manifold gaskets. I don't know about your 3rd generation V8 model but on my 2nd generation V6 model in the stock configuration the engine will start with the IAC valve electrical connector disconnected. However, it will just barely idle or die due to lack of intake air. Air is getting into your intake from somewhere in order for the engine to idle at 2000 rpm. The throttle plate could be sticking partially open. The EGR valve gasket could be leaking. An intake hose could be cracked or broken.

 

[SyberTiger]

I went back and did something I did a number of months ago when I had previously had this problem. Specifically, I cleaned the EGR port inside the throttle body as seen HERE. The throttle plate got cleaned while I was there and the battery was disconnected just to make sure the computer recalibrated everything.

Now, everything seems to be working just fine at the moment. I'm not convinced it was as simple as this as it seems that it is unreasonable that the throttle plate needed a recleaning after only 9 or 10 months since the last time I did it. Don't you find it odd that it would get gummed up so quick?

Anyhow, I'll monitor this. Hopefully, someone with the same engine and model will have a more decisive answer as to precisely what the problem is.

 

[2000StreetRod]

cleaning the EGR port

I read your other thread about cleaning the EGR port before my previous post. I discounted it because the EGR is disabled when the engine is idling so cleaning just the EGR port should have no impact on idle speed. However, if the throttle plate was cleaned when you cleaned the EGR port that could have an impact.

Recirculated exhaust gas while beneficial to pollution reduction contains particles that collect in the intake manifold and disturb smooth airflow. They may also collect on the backside of the throttle plate. A poorly tuned engine and a restrictive exhaust probably increase the particle accumulation. Also, a less effective intake air filter contributes to the build up on the throttle plate as does off road driving.