If the idle stabilizer is getting voltage, then you need to check the continuity of the internal windings of the stabilizer valve. Continuity means that there is a continuous electrical circuit, close to zero resistance, in the windings.

      There are two sets of windings: one set that opens and another set that closes the valve. The connector on the stabilizer has three connectors. Using your ohmmeter, you need to check between the center terminal and each of the outer terminals. There should be continuity at each side. If there is resistance, it means that the windings are probably burnt out or damage, and valve must be replaced.

      The throttle switches tell the computer whether or not it should try to control the idle. If the idle switches are misadjusted or go bad, then if the throttle plate is closed the ECU doesn't even try to control the idle speed. If your diagnosis has brought you to this point, it could be either a bad adjustment, a bad switch, connector or harness, or a more serious harness or ECU problem. There is a trick adapter that allows easily checking the switches, but an ohm meter will do an okay job-it's just a little more work.

      First check to see that the switches are getting voltage. Unplug the connector with the ignition switched on and the car not running, check between the center terminal and ground for battery voltage, about 12V. Take care not to damage the connector. The intake manifold is a good ground. If there's voltage to the switches, proceed with checking the switches. If not, go back to checking
the harness, ECU, or spend more time with the Bentley Manual.

      Check at the switch connector for continuity between the center terminal and each of the outer terminals. One is the idle switch, the other the full throttle switch. At idle, one should have continuity. At full throttle, the other should. Check the idle switch by opening the throttle about half way and then slowly letting it close. You should hear a tiny click as it comes to rest.

      If you find that the full throttle switch has continuity at full throttle by manually opening the throttle valve, but the idle switch does not have continuity with the throttle closed, it may be a matter of adjustment. The switch should close at between .006 and .020-inch from the throttle stop (.15 to.5 mm). If it doesn't, try adjusting it by loosening the switch mounting screws and moving it slightly.

      Other possible problems are damage or cracked wires in the switch harness-more common on 8-valve engines. The wiring can be repaired or the switches replaced.

      If you've had to follow the procedure down to this point, things must be in pretty bad shape, and you may want to talk to an expert before digging deeper. Make sure you've paid attention to detail, and followed each step: patience is a virtue when it comes to automotive diagnostics .
      If you've already solved the problem,
then double check the idle duty cycle following the above procedure, and take time for a cold one. Congratulations. Ron Wood left us with these words: "I have never seen a bad ECU causing an idle problem. Following this procedure
will cure almost all the problems you are likely to encounter."
      Our thanks to guru Ron and the experts at VW Specialties for developing this test procedure.