Here's one for the pros.
I finally got to the checking of the ISV tonight as part of the intake job. Typically, there was the black sticky goo in place, however, when I tested with the 9 volt battery, ......nothing, so, out to the garage and onto the car battery...still nothing....WD 40 and wait, and ... you guessed it ....nothing.
OK, so by the scientific method, we've now determined that the refresh just got much more expensive.....but here's the weird bit...the car seemed be idling pretty much fine before the project started. There was the odd episode of sudden low idle but nothing of any consequence.
Anybody have any thoughts on why/how this valve could be stuck in the closed position and no effects?

 

I assume that ISV = Idle Speed Valve. This valve opens as a function of the duty cycle (on-time) of a constant 100Hz signal. There is 12V applied to the ISV via the LH relay as the "12V source on" switch, and the LH fuel injection controller (pin 33) provides the ground path.

So, the proper test does require a 100 Hz signal, vary the duty cycle and that changes how much it opens. Applying a constant voltage may burn it out.

Verify 12V when the ignition is on. Verify that the ground path runs to LH connector position 33.

 

Hi Rich,
It's out of the car and in the basement.
I just used brief shots of 12V off the battery. No movement whatsoever.
Stuck solid as far as I can tell.

 

Yes, it should jump open with a peck of voltage. If it is stuck after spraying with a cleaner, it is likely dead.

 

My old ISV (replaced it anyway as PM) would open and close very smartly with just a 9V battery applied off the car.

Sounds like yours is faulty. I wonder if throttle cable is adjusted slightly off so that the throttle plate is not closing completely at idle?

 

The default position when not powered leaves a small slot open so the car can idle with it not receiving power, not necessarily idle well but it does get some air. I don't think they are capable of truly shutting off all air flow.

 

yes. This is a feature to offer some resilience. Like a limp mode but this is for some idle behavior.
regards
Theo