How can I test my Idle Control Valve?

Wrecked944 · 12-31-2005, 01:01 PM

My 964 idles VERY low and even stalls when it is cold. It has 12 new ignition wires (thanks to Chris Bennet) and 2 new caps and a new air filter. So I am guessing (emphasis on "guessing") that the ICV may be bad. So I removed it and cleaned it thoroughly (apparently a "dirty" ICV is a common 964 problem). But while it is out, I wonder if I can actually test it. I mean, I don't even know how the damned thing is supposed to operate. And if it can't be bench tested, then would using a short hose to bypass the ICV (and thus leave the idle curcuit open) help me learn anything? I'm guessing running a bypass hose might make the car run better at idle but run worse (i.e. leaner) at all other rpms. Does this make sense or am I trying to hard?

BTW - A new ICV costs $160+ so I'd really like to diagnose it before simply replacing it.

Nine9six · Nine9six's Garage

Did you try adjusting the idle?
Do a search on ICV, I have read where voltage readings are one way of testing.
When hooked up, you should hear it whirring as you turn the ignition to the start position.

ischmitz · ischmitz's Garage

The WSM describes a test procedure: You need an oscilloscope and measure the voltage on pin 1 and 2 while the car is idling. I think you need a special test plug (male female with test leads) to get to it while the it is connected to the ISP. You should see a square wave pattern with about 100 Hz. The duty cycle should change when you switch on loads such as high-beams, AC compressor, etc while the idle stays constant. At the same time you should be able to hear the ISP humming. If there is no humming it is bad. I haven't heard of them going bad very often.

A simple test is to disconnect the two-lead plug during idle. If the engine dies it sort of tells you that the ISP is working fine.

The idle speed positioner is an electrically actuated valve. The inner part of the axle rotates letting more or less air pass depending on the duty cycle of the driving signal. If you take it out and bridge it with a tube your car won't start because it gets way too much air.

For poor idle I would first check the idle micro-switch on the throttle body and make sure it engages properly. Your 89 does not have the CEL yet. So you won't notice if it fails to engage when you lift off the throttle. A poorly lubed throttle body mechanism is all it takes to cause problems here.

Next check and adjust the idle base mixture: There is a bypass adjustment allen screw in the AFM. You need to adjust with a CO meter. Some say the basic adjustment it too rich and backing out the screw by 4 turns improves idle stability.

The idle speed itself can not be adjusted on a 964. It is defined in the DME code.

Hope that helps,
Ingo

Hope that helps.
Ingo

Bill Verburg · Bill Verburg's Garage

The ISV does get clogged up w/ oily deposits, you can clean it w/ brake cleaner, be sure that the inner flap rotates freely. You can apply a low voltage signal to the contacts to see if the flap rotates but the usual issue w/ these after many miles and years(besides clogging) is that the internal electical contacts wear out around the correct normal idle position.

The only cure that I know of is to replace the ISV.

anh911 · 01-02-2006, 10:37 AM

I agree with Bill, if it's gummy clean it out and try that, also from another thread on fuel filter changes, (yes was a 3.2 but still DME car) Car was stalling before changed the fuel filter. Changing Fuel Filter

ianc · 01-02-2006, 02:55 PM

Quote:

A simple test is to disconnect the two-lead plug during idle. If the engine dies it sort of tells you that the ISP is working fine

Hmmm... Is that true? I pulled the plug on my 3.2, but the idle didn't change much. I can hear the microswitch engaging at idle. Why would it die?

ianc

ischmitz · ischmitz's Garage

I don't know much about the 3.2 and how it does the idle stabilization. Does it use the same actuator like on a 3.6? On my 3.6 the engine starts to hunt terribly when I unplug the ICP connector. But my engine is idle-challenged anyways due to hotter cams and the light flywheel for the 915. Both tend to destabilize the idle.

Cheers,
Ingo

JasonAndreas · 01-03-2006, 11:46 PM

Quote:

Originally posted by Bill Verburg
The only cure that I know of is to replace the ISV.

Did replacing the ISV cure your 600rpm idle?

Janus,
I'm going to be in Woostah on thursday night, I can lend you a functioning ISV for a few hours if you want it.

Wrecked944 · 01-05-2006, 02:01 PM

I JUST got a call from my local dealer telling me they found the problem with my idle. Turns out the car had a small vacuum leak. It seems the intake boot was not fully sealed up in a place where you normally can't see it. Just a little leakage was all it took to make the car idle so poorly.

Thanks to all who offered advice (and JasonAndreas for offering the use of an ISV)!

ianc · 01-05-2006, 02:14 PM

Quote:

Turns out the car had a small vacuum leak. It seems the intake boot was not fully sealed up in a place where you normally can't see it. Just a little leakage was all it took to make the car idle so poorly.

Nice, but I don't understand why the ISV wouldn't correct for that if it was functioning correctly. I understand there's a 'window' that the device can only correct within, but I would think a small vacuum leak should be doable? I wonder if your ISV is working properly...

ianc

Wrecked944 · 01-06-2006, 07:39 AM

Good point, ianc. I picked up the car today and posed that question. They said they also cleaned the ISV valve. So it may have been caused by a combination of the two malfunctions. My mechanical skills are below "beginner" so it is entirely possible that I didn't clean the ISV enough or didn't use the right chemicals. And I can report the car runs GREAT now. Sometimes I forget how much fun it is.