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914World.com _ 914World Garage _ TPS, contact arm repair

Posted by: larss Sep 30 2014, 12:41 PM

I fitted a used 2.0 throttle body on my 1911cc and this caused some bucking when accelerating and also when going off the pedal (ran fine with my old 1.7 TB).
Switched to another used 2.0 TB but the same symptoms.
After some fault finding it showed to be the TPS, on the outermost contact arm, the contact "point" (which has a rounded shape when new) had worn down and become flat. The diameter of the contact area had become so wide that it made contact to two tracks on the zig-zag tracks on the same time. This made the ECU to give strange extra injector pulses on accel but also pulses when going off the pedal.
It was easy to identify this with the ignition on and slolwy moving the throttle (engine off) there should be 20 clicks from the injectors when accelerating and none att decel.
It was hard to see this with the multimeter, easier with at test lamp and a battery.

The contact track dont look to worn and it did not help at all to move the contact arm a little to a new path.

I had an old 1.7 TB with a good contact arm which I cut 5mm of the tip and soldered under the old one on the 2.0 TB and the problem was solved.

My question is if this is the 1st thing that normally worns out in a TB (since I had two TBs with exactely the same symptom) and if there is any source for new contact arms?

/Lars S

IPB Image

Posted by: StratPlayer Sep 30 2014, 02:45 PM

Don't think there is a new source for the contact arm. There is a vendor here on the site that sells new reproductions of the TPS at a reasonable price. Check the vendor section for this item.

Posted by: davesprinkle Sep 30 2014, 08:56 PM

I've got replacement boards, but I have no parts to repair the wiper arm, unfortunately.

Good job diagnosing and fixing the problem. Resourceful.