High Idle - Quick Question about The IAC Valve on a 2.9

[jhammel85]

I'm hunting down a high idle for my truck that suddenly appeared after work tonight. When in drive (automatic), no matter how cold / warm, it runs at about 1300 or so. In park its almost 2000...

I sprayed carb cleaner around all lines with no luck. I pulled the plug on the IAC valve to see if it changed and it didnt.

That being said, I pulled the IAC valve and had someone turn the key so I could see it move. The Plunger nudges back and forwards but never really moves much. Is that normal? It doesnt move too much at all really..

I've cleaned it before so I cleaned it out again and fired the truck back up with no luck. I've sprayed all possible areas where there could be a vac leak (including the upper and lower intake area) with no rpm flare..Theres also plenty of antifreeze in the radiator and the heat blows red hot in the cab at idle.

I guess my question is the IAC operating normal? Any ideas anyone?

 

[Earl43P]

Whack the IAC against the palm of your hand and you can feel the plunger traveling along that shaft, should make a thwock sound. Spray it out, thwock it a bunch of times in both directions and do that key on test again / install it.


The idle should change when you disconnect/reconnect it.

 

[adsm08]

Sounds like the IAC is stuck. It should drop off a lot if not die altogether when the IAC is unplugged.

 

[jhammel85]

Thanks for replying.

Another thing to throw out there is that when I got home yesterday, coolant burped into the overflow tank. The electronic gauge showed normal like it always does. Once everything cooled down, it was a bit low. When looking down inside, it was maybe... 3/4 full? It's been filled back up but the computer was not reset. I should do that incase maybe this whole thing is a fluke with the Engine Coolant sensor. I'll let it sit off the battery while I'm at work today.

As far as the IAC goes, it could very well be it. It doesnt move much at all and when it does, it's not very smooth. I've always had a start up issue with the truck where once started, it'll run rich, hunt for idle and then find it with no problems at all after that.

It figures...I just sold my spare IAC I just ordered a new one (along with the gasket. My good buddy "previous owner" didnt have one there). I'll post up the results of unplugging the battery and the new IAC as soon as I can. I hate it when these threads arent resolved!


Thanks again!

 

[jhammel85]

Alright so I just unplugged the EEC for a bit...

But before that, I played with it some more. I see that the ball inside (inbetween both ports) does move, just not very nicely. It nudges and thats about it. With it connected to the upper intake and the truck running, I can unplug it all I want with no change at all. I think the solenoid is on its way out..

Either way, If the EC sensor was to blame for some low coolant, having the power off the battery for a bit should clear that. My money is on this valve being bad though..

 

[jhammel85]

With a new IAC, it's all better! I noticed that the old one would nudge and only move once. the new one looks like it moves at least twice when it 1st comes on with the key. The truck is 100% better. I actually had to turn down the idle a little bit still. I think the old one was stuck for a while and it progressively got worse. Now it's idling at a happy 850 (auto) and all seems well!

Another oddity is that the vacuum is a bit better now. It makes sense if the valve was giving me issues I guess...

Thanks for everyones help.