I have a 85 jetta GLI and when I remove the throttle from 1-2K rpm's instead of coming back to 800-900 rpm and stopping there the engine will sometimes overshoot and go down to 500 - 600 rpm and then come back to 800 - 900 rpm's. Any ideas?
Bruce
I'm not sure, but (like my fox) there may be an 'idle correction valve', which opens if rpms drop below some value... this valve lets more air into the engine to raise rpms. The valve also closes when rpms get above a certain value (i.e. so when you accelerate, the valve will close).
Check your throttle position switches, in particular the one for idle. On my '87 the idle throttle position switch is at the bottom of the throttle body and quite hard to get access to.
Do an audible test first. You will see where the gas pedal wire is connected to the throttle body. Use your hand to manually open and close the throttle and listen for a click as the throttle closes. That is the switch. If you hear no click, chances are the switch is broken.
The wire harness to the TB switches is connected to a connector mounted to a bracket at the rear of the throttle body. You can unplug the harness and measure the switches here (there is a spring clicp on the connector, push it in with your thumb to unplug the connector). Some models have 2 terminals and the idle and wide open switches are in parallel. I believe the '85 had three terminals, common, wide open and idle. Measure all three combinations of pins with an ohmmeter (or diode tester). One combination should show continuity at idle only, another combination should show continuity at wide open throttle only.
While scavenging for parts at the local junk yard I noticed that on quite a few Golfs/ Jettas of the older vintage the idle switch was broken (plunger broken off the switch).
If you have a broken switch you can get a new set of switches at the dealer for around $117 or you can hit the junk yards. I did the latter and was not able to find a complete set with two working switches and a three pin connector. I ended up getting a set with the two terminal connector (the switches are the same as for the three terminal set, only the wiring is different) from a newer car. I then spliced in the "new" idle switch onto my old harness.
To make it easier to work >
I fixed this switch several months ago and it did stop the hunting, but this is a different problem. Thanks for the idea.
Bruce
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