Throttle position sensor check and fix
written by: maxAbout this Guide
Checking and repairing the TPS (throttle position sensor) on OBD-I Volkswagen Golfs/Jettas.
Step 1: Background info
I felt the need to write this up because of the hassle I went through with my 1995 Jetta not running right. To make a long story short, the Jetta ran like total crap without the check engine light coming on and without the ECU storing any fault codes. It got so bad that the car would hardly run - the RPMs would cyclically surge and then drop, constantly. I eventually decided to check the throttle position sensor because I ran out of other ideas. Well, the sensor ended up being bad but I was able to repair it. Take note, OBD-I VW owners - if your TPS goes bad, it will not throw the check engine light on.
Step 2: Test sensor at ECU harness
Using something for test pins (I used pieces of copper core from some solid core wire), we'll start by checking the sensor at the harness that connects to the ECU. The ECU connector on an A3 Golf or Jetta will be located in the rain tray, on the passenger's side. Refer to your Bentley manual to see which pins you need to test in your connector - it may vary. There will be two tests, involving different pins. Across one set of pins, you should get increasing resistance as the throttle is opened. Across another set of pins, you should get decreasing resistance as the throttle is opened. If you get the correct readings, then stop now because your TPS checks out fine. If you get incorrect readings, then continue to the next step.
Step 3: Test sensor at sensor itself
Now locate the throttle position sensor itself (on 4 cylinder OBD-I Golfs/Jettas, it will be out in plain view mounted on the throttle body) and pull the connector off from it. Perform the same tests at the terminals of the sensor itself. If you get correct readings from the test you performed at the ECU connector, then you have a wiring problem between the sensor and the ECU connector. If you still have incorrect readings, then continue to the next step.
Step 4: What's the problem?
If either (or both) of your readings are giving you an open circuit, then there is hope for repairing the sensor. The sensor has checked out bad at this point, so you don't have anything to lose by cutting it open and attempting repair. It may save you having to buy a new sensor. If you're readings are incorrect, but not open circuits, then the sensor will not likely be fixable (although, feel free to try). If you're ready to attempt a repair, then remove the throttle body to get access to the sensor's mounting screws.
Step 5: The surgery begins
Once I had my sensor removed from the throttle body,I cut the top of it off using a dremel. When you see inside of this thing, you'll see how it works. There really isn't much to it - just metal fingers that pass along carbon tracks. In my case, I had open circuits on both tests and I could see right away that the metal fingers were not even making contact with the carbon tracks.
Step 6: My fix
The fix in my case was simply to bend the metal fingers a little bit so that they made contact again. This was easy, as the rotating plastic piece that hold the fingers will pop right out. Your situation may require a different solution, but these things are so simple inside that if a fix is possible, it will probably be quite obvious.
Step 7: Closing up
I used some industrial rubber cement to reassemble my sensor, and after that I had no more problems. The sensor checked out fine, and the car ran like it should again. Hopefully this works for you!