skytrain4

My ’92 LS 400 engine started revving up and down between 1100 and 2000 rpm. The high idle occurred only in park and neutral. It did this even at cold startup. I immediately started searching for this problem on this and two other forums. After A couple of hours of research I decided the problem could only be the ISC Valve. I fixed it, and the car idols smoothly now. I did not replace the ISC valve at a cost of $700. Instead, I took it apart and fixed it with a squirt of WD40.

The ISC valve is the little round black object located on the front of the upper Intake Manifold, underneath the black plastic spark plug wire cover. 3 screws hold the ISC Valve on and there is an electrical connection located bottom left. There is no need to drain the coolant or disconnect the water and air hoses or unbolt the metal base where those lines connect. Simply remove the 3 screws, disconnect the electrical connection, and pull the ISC valve straight back and out.

Once out, plug the electrical connector to the ISC valve and start the car. The car will run for only a few seconds before dying because of the gaping hole sucking air into the intake. But, it will run long enough to observe the little metal valve (tit) move out and in. If it moves about 1/4 inch, the valve is good. Mine didn’t move at all. With the ignition in ACC, I checked and there was 12 volts on the two center pins of the connector plug. The problem had to be in the ISC valve.

I took the ISC valve apart by removing the 3 little screws and pulling the shaft out of the black casing. Then, I held the tit and unscrewed it out of the magnetic drum. There are 2 wheel-shaped bearings, one on each end of the magnetic drum. Both bearings should spin freely. One did and one did not. I sprayed WD40 on it and worked it in by spinning both bearings until they spun smoothly. I wiped off the excess WD40 before putting the valve back together. I connected the valve electrically, started the car, and the tit moved out and back in. I put everything back together and the car idles perfect.

This took less than an hour, and I saved $700.

superglide

Sweet!

Congrats on the DIY, and the troubleshoot.

Always a good feeling to do something yourself and to save $700 on top is icing on the cake.

SENSAY813

Do you mean idle air control valve? Never heard of isc ?

Legender

Nice find and thanks for sharing your excellent results.