Fast Idle

[Snowcone]

Over the past couple of weeks my 2002 4.6 Explorer has been idling at around 1800 rpm in neutral - hot and cold.
I did search a believe the IAC valve is the culprit.
This valve is not available in Australia so I am at the mercy of the dollar conversion and expensive overseas freight costs resulting in me having to pay double what you guys pay there for a valve so I wanted to confirm if this is the probable cause before outlaying the money.
the search also said to avoid copies of the IAC and only use a Motorcraft one.
I tried cleaning it at the weekend with carby cleaner but nothing changed. I can confirm that when I unplug the IAC the idle drops down to 500 rpm immediately.
Is it possible something else is influencing the IAC or is it a stand alone valve that is just gone rogue on me?

 

[1996EB]

Have you scanned your vehicle for any trouble codes? I had to change my IAC valve a few years back (03 4.6L), but I'm pretty sure that I had a trouble code(s) that pointed toward the IAC. I also had basically the opposite problem of yours- idle dropping too low and stalling. You may also want to clean your MAF sensor, before you buy a new double-cost IAC valve. Make sure to use a proper cleaner, as the MAF sensor wires are sensitive. Good idea to go with Motorcraft if you decide to buy the IAC valve.

 

[Joe in NY]

Well, I would say your IAC is working fine if you unplug it and idle drops to 500 rpm then back up to 1800 rpm when you plug it in.

This shows that it is doing from 0% to 100% perfectly... It also shows that the PCM is commanding 100% for some reason. You most likely have other issues.

 

[SyberTiger]

I disagree...it probably is the IAC valve. They are definitely known to go out in common fashion. I had the same problem too...you can search my threads to see my original comments. When I had the problem my idle was similar to yours or even higher...I ended up unplugging the thing to bring the idle down but I ended up driving it a few miles to get home using two feet to keep the idle going at stop lights. When I replaced the IAC it magically fixed the problem. Also, a VERY important note...don't bother with the after market variety. Go with genuine Motocraft part on this one as the after market ones are notorious for failing. This is the one part you don't want to go after market.

Before you go to the expense of the IAC...not only make sure you clean it well (see my posts on how to clean it)....but make sure you clean the intake as best you can. Again, if you look at my posts on the subject of "idle" problems you'll see a write-up I did on cleaning the intake which denotes a very strange buildup of gunk inside the intake. You look like you have the same year and engine as I do. Also, disconnect the battery when doing all the cleaning to reset the computer.

Good luck and let us know how it turns out.

 

[Snowcone]

When I took the IAC off there was a lot of carbon inside the throttle body hole.
The workshop manual I have says not to clean the throttle body with carby cleaner etc as the throttle body has a special coating on it.
Not sure it this is BS as carby cleaner is what i would be using if I did it.

 

[SyberTiger]

You use a product called "Throttle Body Cleaner". Yes, it is different than Carb Cleaner. Here's some reading material for you.

How to: Clean the MAF Sensor and the IAC Valve (2002 - 2003)

IAC Problem: How many RPM's does your vehicle IDLE at?

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

 

[Snowcone]

I replaced the IAC valve and also did a battery disconnect.
Idles perfect now so problem solved