Last Lemming

So this is for an 86 turbo, but I think this applies across the range in principle.

I just replaced all my vacuum hoses, the venturi (I'm not doing the delete), and a new ICV. I've double-checked all my connections and the routing. I've also done a smoke test on the system and there are no leaks. I also have a rebuilt throttle body a year or so ago and that was working fine up till this point. the TPS is also working fine based on the tests in Clarks.

I have an issue trying to set idle. Currently, it's running about 1100 RPM after start and after idling from cold for 5-10 minutes.

I set the stop screw on for the throttle plate, but when I plug in the jumpers across B/C in the test port nothing happens. The RPM remains constant - no change. Turning the idle mixture screw all the down doesn't change anything, the engine will continue at the same high RPM.

I'm wondering if the ICV might not be getting the signals it's supposed to get. So the question is how do you test the wiring and signal going to the ICV at the plug? What should I be looking for on a multimeter?

Assuming there are no vacuum leaks what else should I be looking for if not the wiring?

Zirconocene

I know you said the ICV is new, but I would check that, as well. Applying momentary power to the plug should result in some clicking from the valve that indicates it's opening as intended.

For checking the wiring to the ICV itself, what about using a noid or timing light? As I understand the way the ICV works, it's not held open at a particular set point, but rather opens and closes quickly to replicate an average opening, depending on AF needs. This is why I think a timing light might be helpful; you should be able to see the flashing of the signal to the ICV when the engine is cold.

The other thing that you might want to look into is the butterfly in the throttle body. A friend of mine just went through this on a 928 and the disc in the throttle body was set sort of crooked, and asymmetric, causing air to leak by that was hard to find via a smoke machine.

If you're interested, I can add a link.

Good luck

walfreyydo

This is for a late model IACV (variable not binary like older models). You should be able to back probe the connector, or use aligator clips on the connector to measure the voltage. Voltage on these is variable, the more voltage, the more the valve opens (up to 12V for fully open). I dont think it requires a timing light or noid light. Just a multimeter.

As the engine warms up, voltage should decrease, slowly closing the valve. I do believe there is always *some* voltage keeping the valve open at idle, regardless of temp, but a cold engine should command more voltage than a fully warm engine.

For what its worth, my engine idles at 1000-1100 RPM, so it does feel to me like you are splitting hairs with your worries about idle speed.

I do not know what the voltage "spec" is for a cold vs fully warm engine going to the IACV.. or if there is even a specific voltage if for instance it varies based on different conditions (cold engine hot day, cold day cold engine, etc may all result in different voltages to meet a specific target RPM, ie closed loop idle). Because of that, it may not be as straightforward as saying, at this coolant temp, the IACV has this voltage (otherwise known as open loop idle). Im not sure if OEM motronic is open loop or closed loop idle. I think understanding this would be critical to knowing the target voltage ranges.\

Above information was wrong, but George posted some really good info over at the Pelican forums, which pertains to the late model IACV: http://forums.pelicanparts.com/porsc...-question.html

You might have to do some googling on this, or see if there is any old threads or resources showing what normal voltage should be (Factory Service Manual perhaps, available for free in PDF form) and if that voltage varies based on IAT, coolant temp, etc or if its just a standard voltage for a given coolant temp.

There may also be other factors affecting your idle speed, if indeed the car does run in closed loop idle, such as the IAT sensor within the AFM working properly or not. Also, it might be worth verifying that the throttle plate is fully closed, or if its sticking open slightly, as this will increase your idle speed due to the small amount of air moving past your throttle plate.

Last Lemming

Thanks for the info.

the thing that puzzles me in all this is jumping the test port has no effect on the idle whatsoever. It used to bore I started having this issue.

Zirconocene

I had to make sure, but those idle numbers seemed pretty high to me. Here's what Clark's has to say about things: http://www.clarks-garage.com/shop-manual/fuel-08.htm

Cheers

walfreyydo

From Clarks
I have an S2 so this explains it, but my car does idle at approx 1k. Different system than the NA's and turbos apparently