High idle issues;
I started at the point with the crank at 0-degrees TDC and ignition distributor @ cylinder one.

I can retard the timing to bring the idle down but it runs/sounds crappy. Put it back to TDC with ignition distributor mark on cylinder one.

I did the smoke test but I ran out of smoke. I had enough to check for obvious signs or huge leaks. I will do the smoke again to detail any small leaks should there be any. My main concern was to find any large leaks with the larger hoses that connect at the injector holders, ICV boots, air intake boot, donuts or anything under the intake.

Can someone explain how the ICV works or how it functions? How to diagnose further than I have done already?


At first, when I checked the ICV, there was no voltage. The overload protection relay was fine and when testing out the ICU (or ICM), voltage went in but none came out. I changed the ICU. At that point I had battery voltage at the ICV using a test light. After the warm up, the test light would hardly glow which indicated lower a voltage. All the while I still had high idle, even after disconnecting the power to ICV.

Today, I removed the ICV and cleaned it up. Powered with external 12volts to check operation and it appears fine. Put the ICV back and started the motor. I decided to check voltage with a volt meter this time. It's odd, while I checked for voltage on the back side of the ICV harness, at the ICV pins, I couldn't get a steady reading. The voltage changed all over the place. So I figured, let me check with the wire harness connector removed [ I removed just the top barrel connector which is (+) and kept the bottom barrel connector (-) on the ICV ] and I got battery voltage which I expected. Put the top barrel connector back on and got whacky voltages again. After warming up I did the same procedure, except this time, with both barrel connectors on the ICV and got a voltage reading of .99 V. When I removed the top barrel connector as before, I got battery voltage again. All the while the motor still idling at 1500.

~I removed the the throttle body linkage to see if it might be stuck open a little somewhere, nope-
~I cleaned the ICV and not sticking. Checked operation off vehicle and looks good-
~No change in idle with ICV harness connector on or off-
~No major vac leaks that I could find but I do have to smoke again-

I am thinking there may still be an issue at the ICU since it doesn't drop the voltage with the harness disconnected - unless I am doing something wrong with how I am taking my readings. There could still be a bad temp sensor feeding/not feeding the ICU, then not giving proper (3-5V) voltage to ICV, I will check that next. But still there was no change of idle with or without the voltage on the ICV.

Not sure which way to go on this but I am thinking of checking pressures at the WUR and rebuilding it if need be.

Any help would be fantastic!!

Thanks !!

The idle control valve is electronically controlled and must be energized to reduce the idle speed. If the control module is acting up or the OVP relay has failed, the default strategy is to leave the ICV open and default to a high idle.

Check out your control module for the ICV, you probably have broken solder joints, it's a very common issue. It will cause erratic operation and make you pull your hair out trying to nail it down!

The control circuit of the ICV is transistorized in nature, you must measure voltage with it connected to the ICV, you can't accurately measure the circuit voltage just by probing the plug. You can test the ICV itself by applying 12V directly to the terminals (make sure you have the plug disconnected). The engine RPM should noticeably reduce and possibly stall.

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Thanks Diseasel300 !

Well, that did it. Applied 12 volts directly to the ICV and the motor stalled out. So no issue with the ICV that I can tell. I am not sure how to measure voltage since it is all over the place or shows a very low value. I'll look into that more.

I am looking at the ICU which I thought was good but apparently not. Still not sure how to test the ICU. I understand there are some transistors that do go bad. I am going to check the three transistors on the board to see if they are bad and then replace them if so.

One step at a time...

Measuring the operating voltage of the ICV will not yield usable information. The ICV is driven by changes in current: 0mA>open, 1000mA>closed. To achieve the current variation the ICU modulates the width of the grounding pulse, hence PWM @ about 200 Hz. An O-scope will be of help.

here's the factory info-

https://www.startekinfo.com/StarTek/outside/12253/disc%202/program/Engine/107/M116_38/07.3-112.pdf

good luck, chuck.