I've been attempting to figure out why the idle stabilizer valve on my car doesn't seem to be working. What it does is stabilizes the idle at cold temperatures. Without it, the car wants to stall, idling around 400rpm when the engine is first turned on in the cold. The Valve either allows more air in or cuts the air supply to adjust the idle speed higher until the engine is warm. My car idles far too low in the winter time, which is in direct opposition to the other 944 in the driveway which idles stable at 1000 even after not being started for two months. I'm exploring the possibilities why.

This is the valve itself. It's hard to see, but there's a door that opens and closes inside it when a certain signal is sent from the computer (cold engine).

Here are the tests and conclusions I've drawn so far:

• From the old thread located here, power was delivered by a 9V battery to the valve and the valve's door operated perfectly. Reversing the polarity and the door opened back up. This leads me to believe that the ISV is working properly and functional electrically.
• When the starter is on the ignition setting with the car off, the ISV should be vibrating. This can easily be felt with your fingers. With the car on, there's just too much other vibration to tell. All tests I've done show that the ISV is not vibrating. I can't for the life of me feel anything leading me to the possibility that it's not being fed power from the computer.
• Further reading on the subject leads to the possibility that the transistors in the computer are fried, often as the result of overheating. This has been reported in other 944s, 911s, and BMWs on forums on the net. They all share the ON588 transistor set. I cracked open my computer and didn't see anything noticably burned or broken. The ON588's look fine, but transistors can fail on the inside without any visible scarring on the outside. I'd have to run some multimeter tests on the things. Which I did.
• As I write this, I'm still awaiting confirmation that I'm testing them properly. But as far as I can tell, one or both of them is failing the test, not regulating the current the way they're supposed to. If this is the case, then the ISV probably isn't getting the power is needs to operate correctly which would explain everything.

I'll post back more when I know more. I'd love for my car to run properly when it's cold. Nothing worse than having to sit on the gas pedal for two minutes before being able to back out of the driveway because it'll stall when you let up to put it in gear.