hwyengr

Sadly, you can’t. The ‘85/‘86 ISV is a miserable little design. It’s an unsprung free-swinging plate that’s driven by electromagnets. Voltage to one side swings it open, voltage to the other pulls it shut. By modulating the signal to both poles, the valve opening size is controlled.

But that means that unless the valve is full open or full shut, it’s constantly vibrating back and forth in the valve body, which wears it down until it gets stuck in one spot. That’s why it can burn out the LH idle circuit, because it wants to move the little plate, it’s putting constant voltage on one side to make an adjustment that never actually happens.

Fly911

So since my ISV is new, does that mean that the driving circuit in the LH ECU is burned out?
Before I changed the ISV, the old one was making a crazy clanking noise, like it was opening and closing very rapidly. The new one doesn't make any noise, but I don't know if it actually works. How can I check or test that?

hwyengr

You can test the ISV off the car by hooking it’s pins up to a 9V battery. If the plate swings freely in both directions it should be good. There have been reports of them DOA out of the box, so being new isn’t definitely a guarantee. Did you find a Bosch valve?

Other than sending the LH out for bench testing, I don’t know if there’s a way to test it on the car. I have heard that the “test” is whether you can feel the ISV vibrating when the engine runs, but how you can tell that over regular engine vibrations is beyond me.

JayPoorJay

Interesting... And good find.

If you remove the air box, it's underside and all, then the MAF of course, using a light it might be possible to disconnect the electrics, get a screw on the clamp that holds it and pull it out with superficial surgery. Depends on where that clamp screw is... And, like others have said test it with less than 12v.

I changed my ISV with Rodgers aftermarket replacement. A good thing at a good cost. In the lead up to that heard about the potential for burning the computer which certainly put a fear in me. I hope that that ain't what you're looking at! Really.

I would hope for the best - might just be the wiring!!! It is old and lives in a pretty hostile environment. I struggled with finding a way to test current and signal with everything connected,,, and can't remember how I did it (Merlin helped me). I do remember that key ON isn't enough to get (and read) a signal from the brains to the unit,,, I believe the car needs to be running - or at least cranking. I wish I took better NOTES! Or any at all, lol