Severe High idle problem

O

oldprotrac

Spoolin Fool
Joined
Oct 6, 2006
Hi guys,

I am having a really bad idle problem. My car idles 1300RPM or higher.:( I have done the IAC reset procedure multiple times. Replaced all gaskets on upper plenum and intake. traced out all vacuum lines and eliminated those as possible high idle issues. The IAC is at zero at idle with the set screw all the way back on the throttle body, no matter were the tps is at it idles high. I can disconnect the IAC and try to adjust idle with throttle body and it does nothing below 1200RPM. How can i tell if the IAC motor is bad??? It moves off of zero when crusing but at idle it drops back to zero. Is 0 fully closed or fully open??? I have been struggling with this for a good while now, any help or ideas would be great.:(
 
IAC of 0 means that the ECM is "commanding" 0 air from the IAC valve. This is correct, the IAC number would go up during idle if the ECM needs air to maintain normal idle.

In your case, more air is getting in than needed to maintian idle. If you're certain that you've plugged all possible vacuum leaks, and the throttle blade is physically closed, then you may consider that the IAC valve is stuck open. I would expect that you'd get an SES code if this happens, though. Remove the vac lines from the vac block and physically block them. Take off the up-pipe and verify that the throttle blade is actually closed, etc etc. Process of elimination. Then remove the IAC and find a way to block off the hole and see if it will still idles high or at all. Just some thoughts.
 
Ensure that ALL connections from the throttle body back through the intercooler/turbo/MAF all the way to the filter are solid and not leaking. MAF hooked up?
 
I havent just plugged the vacuum block but i will try that too. Just last week i installed my new Precision turbo upper plenum and 70MM throttlebody thinking the stock unit was leaking air, but both the stock and 70MM do the same thing idle at 1200 or higher.

Dave, yes the MAF is hooked up and working. All of the pipes and fittings are tight.
 
I'd suspect the IAC also...it's allowing more air in than it says.

I think you'll be able to get your idle down by screwing the minimum air screw IN more. Open up the throttle blade. Try it, maybe you'll like it.:biggrin:
 
This thing is causing me fits. Nothing i seem to do helps. The chip has the idle set at 875RPM also.
 
Make sure your TPS is set to less than .5v at idle or you will experience what you stated above.

Neal
 
It's either a faulty IAC or a vacuum leak. Do you have a vacuum brake booster? It could be the source of a leak.
 
Im almost positive on an IAC, or a huge vacume leak. Commanding 0 and it, not dieing means that either the motor is dead, and is not going anywhere, or there is a very big leak somewhere! We have a tester at work that has a light that goes on the IAC signal wire telling if the computer wants open or closed, and then there is a switch box that plugs into the IAC to let you manualy controll the IAC to tell if it is working or not. Maybe you can check with a dealership in the area and see if they have one!

,Dan
 
Im going to pull the IAC and apply Power to it to see if i can get it to move. Does anyone have a pinout of the IAC so i know how it works and were to apply power to????
 
The wiring diagram I have shows all four wires going straight back to the ECM.

Lt Blue-Black IAC A LO
Lt Blue-White IAC A HI
Lt Green-White IAC B HI
Lt Green-Black IAC B LO

With that said..... it looks like the two light green wires go to one coil inside the IAC.... and the two light blue wires go to the other one. I would reason that one is an actual variable voltage coming from the ECM and a ground.... when the voltage goes up.... the IAC probably moves. The other pair of wires... is probably 5v and the other a reference to tell the ECM where the IAC actually is..... otherwise it would have no way of Knowing if the IAC had moved or not.....this comparison of where the ECM told it to go... vs where it actually is.... is likely what trips a SES code.

Just an educated guess....

HTH
 
The IAC is a stepping motor, so you can't just apply power to it to make it move. To test it you could remove it from the throttle body then plug it back into the wiring harness and have someone turn the key on while you watch the motor. The pintle should move out then back. The computer actually has no idea where the position of the motor is. What it does is drives the pintle into the seat of the idle port and then backs it off a certain number of counts determined by the program in the chip and then controls idle from there.
 
as asked before ,
did you verify that the tps sensor is still within spec ,
.44v or less
 
Thanks for all of your responses guys. What i finally found was a bad IAC motor. I installed a new IAC and the problem went away. Idles at 825. Thanks again for the help.:biggrin: :D
 
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