is my iac bad?

[spitfire5454]

this is driving me crazy. about a month ago i developed a an idle issue. it would surge in neutral or idle high. so i replaced my intake gaskets and tps sensor. all was fine for a week. since then, my idle will randomly shoot to 1900 in park or neutral, and when in drive, it will accerlerate by itself, causing a lot of brake pressure needed to stop and overheating in traffic. It only does it randomly, but seems to occur when the engine is warm. It never happens first thing in the morning. Ive searched for vaccum leaks extensivly but cant find any. the only thing that makes a difference is if I unhook my IAC. with it unhooked, it will idle at 900 in drive and only 1300 in neutral. But it doesnt want to accelerate by itself, and it doesnt over heat. oddly enough i dont get a CEL with it unhooked. I figured i would for sure. So in summary, it runs much better with it unhooked. Should i replace it? Thanks

[VehiGAZ]

What's IAC stand for?

Sounds like the part is the problem, though (as you have described it).

[mdwyer]

IAC = Idle Air Control. It is a little motor bolted to the side of the throttle body. It uses a screw to move a cone-shaped valve in and out of a hole to allow a metered amount of air around the throttle plate to maintain the correct idle speed.

I was able to make mine start idling okay by taking out my IAC and thoroughly cleaning it and the throttle body with some sensor-safe cleaning spray.

Even so, the VX seems to have a LOT of torque. It still, sometimes, will boost the idle somewhat -- possibly it is being kicked up by the AC compressor -- and it will start to creep away at red lights.

I think keeping a firm foot on the brake is just another VX 'feature'.

Try turning the AC (and by extension, the defroster) off, and see if it still tries to get away from you.

[SilverBullet75]

Hi,
here is a pic of the IAC.

Your symptoms actually sound like the fuel pressure regulator to me. I had the same symptoms, and after replacing the regulator all was good.
The IAC will cause the engine not to idle (with no code thrown)...
At least, these have been my experiences... so I won't speak for others.

http://www.vehicross.info/gallery/data/500/thumbs/engine.jpg (http://www.vehicross.info/gallery/showphoto.php?photo=13185)

[AndyC]

Humm sounds just like what I experienced this weekend. My engine light is one so I do have a code there. I'll check tonight and post up.

[WormGod]

Interesting thing last night while I cleaned mine up. Dismantled and cleaned the IAC and since I was in there, decided to go ahead and clean up the TPS too. WOW! I have never taken that off. It was horrendous in there. Looked like very fine dirt caked all over the interior. I have only been offroad maybe twice in her life and that was at a beach, so anyone who takes theirs offroad may want to actually clean this out more than occasionally. No gasket, just 2 screws, and it appears dirt has pretty easy access to get inside.

This snippet may be of some aid in some possible throttle sticking. Unknown how much if any issue it causes since I only JUST came across this last night. *shrug*

[spitfire5454]

So I took it to my mechanic because I was outta ideas they hooked it up to the computer and they assured me it wasn't a vaccum leak. They said the tps sensor was putting out some wierd voltages. They said it needs to be replaced. I told them I replaced it last month. It was a part from autozone. He said he has seen more defective parts from autozone than he can remember. He unplugged it and everything runs just fine. Never did throw a code though. I'm gonna replace it again with a dealer part. Sounds a little fishy though. I've never had a prob with autozone parts. Any thoughts? That was an expensive diagnosis

[etlsport]

where is the tps?

[mdwyer]

where is the tps?

Didn't you get the memo? :bgwo:


The Throttle Position Sensor is on page 6E-450 of the tech manual. You know where the pulleys for the throttle and cruise control cables connect? On the left of the throttle body? Imagine the throttle plate rod going through the center of the throttle body from those pulleys, and exiting the right-hand side. The TPS is the sensor on the other end of that rod.

The tech manual just says it should read .85V at closed throttle, but it doesn't say much else.

[AndyC]

I just checked my IAC and that was pretty clean. I knew it was a Vacuum leak. I could hear it and it appears that my lower common chamber - intake manifold gasket is cracked. Looks like the gasket material is hard plastic-ish and has cracked. Might have hardened from heat ? Who knows. Well a quick fix was some of that silicon insta gasket stuff. I filled the cracks and I'll see tomorrow it that fixed it.
The trouble codes that I pulled from my Scan Gauge II was a 171 originally from the weekend trip and then I cleared them. Before I found the second leak a 171 came up again. Final time no codes came up.