Odd idle problem

[MEGADET0]

Ok, I've searched and read every idle topic on here. I still can't figure this out. I've tried multiple TPS's, two different idle control valves, a MAS off a perfectly running car, replaced most hoses with tight silicon, multiple throttle body assemblies, and I'm still stumped.

The car will start and idle perfectly until I touch the gas. Then it slowly raises to 2500rpm. If I tap the accelerator it comes down to a perfect idle for a few seconds then slowly raises back up. After a minute or so tapping the accelerator to bring it back down, it starts to not drop all the way back to normal before it raises again. I turn off the car and it idles perfectly again untill I touch the gas.

Any ideas anyone? I'm stumped. Thanks for any help.

93 SS Turbo

Casey

[BSOD2600]

When you replaced the throttle body, do you check and/or readjust the TPS?
Cleaned the IAC?
checked for vacuum leaks? what is the inHg when you're idling?

[Legacy777]

Welcome to the BBS.

Any check engine lights? I'd suggest starting with checking the ECU for stored codes, which may help lead you to the problem. You can check the codes via the instructions on my site.

www.surrealmirage.com/subaru/engine.html

If you replaced the TPS and it was not set/adjusted properly that could be causing the problem. Adjust the TPS using these instructions

http://www.main.experiencetherave.com/s ... sting3.jpg

Also, does your throttle body have a screw on the top of it?
http://www.main.experiencetherave.com/subaru/images/tb/

[MEGADET0]

I have not set the TPS to those specs. I will do that soon. I did clean the IAC valve. I've checked for vacuum leaks and can't find any culprits. The vacuum at idle holds at 15 inHg. There is no check engine light. And there is not a screw on the top of the throttle body. Any other thoughts while I'm setting the TPS?

[Legacy777]

How did you clean the IAC valve? Did you remove the top electromagnetic piece on the IAC valve?

You vacuum at idle is pretty low, it should be around 19 inHg. Was that reading taken when the engine was idling ok? What rpm was the engine at? Where are you located?

[MEGADET0]

I used brake cleaner to clean the IAC. I've tried 4 different top sensors on top. I couldn't get any of them to adjust correctly. The vacuum reading was taken with the IAC unplugged. Unplugged, and adjusted all the way to the passenger side the car idles perfectly but has a check engine light obviously. I'm located just south of SLC Utah.

[MEGADET0]

I just confirmed the TPS is adjusted to factory settings. I also changed the coolant temp sensor as a possibility. It's still idling at 2500.

[MEGADET0]

I've traced things down to a wiring issue. The center yellow wire going to the IAC valve had been cut and a new wire was run to a constant 12 volt source. I switched it back to the stock wire to see what it did. Same result. The stock wire does not have a voltage with the ignition on. It should have 10+ volts from what I've been able to dig up in pdf's. Can anyone run through the wiring on that valve and tell me what should go to what? I may be able to bypass a problem point. Thanks for any help.

[Legacy777]

So that middle wire on the IAC valve does not have 12v going to it?

It should have an ignition switched 12v source. That's it. So if it's bad, just wire a new 12v ignition switched source to that middle pin.

[MEGADET0]

I know the center wire needs 12 volts. It had a 12 volt source ran. The car runs the same with or without the 12 volts, which means there is more than just that center wire issue. Subaru wanted $640 for the full harness! I'll try my hand at wiring. Does anyone know what the othervtwo wires run to? Does the center wire adjust voltage depending on RPM to adjust the magnetic field strength in the top sensor to adjust the idle?

[BSOD2600]

Does the center wire adjust voltage depending on RPM to adjust the magnetic field strength in the top sensor to adjust the idle?

The FSM posted in the stuff you need to know forum has full wiring diagrams.

[Legacy777]

The two other pins go to the ECU, which controls the opening & closing of the IAC valve.

As BSOD mentioned, the FSM is in the stuff you need to know forum. Here's the IAC excerpt from that manual with the info you need.

http://www.main.experiencetherave.com/s ... C_Diag.zip