TPS question

[BennSport]

Howdy everyone, I was wondering if the throttle position switch is just a variable resistor? I was trying to test it today as I’ve had an issue with my car bucking in first and second gear during low throttle. As I was testing all my resistance readings were at 0. I assume that means I have a faulty tps but I wanted to get a second opinion. Thanks again!

[Tom]

On the non-turbo cars, there are just 2 switches -- DME pin 2 should be grounded at idle only, and DME pin 3 should be grounded at WOT only. On the turbo, there is an idle switch (off/on) and a potentiometer that tells the KLR how open the throttle is. The KLR then triggers WOT mode when the throttle opening exceeds a certain threshold (~65%). Which car do you have? Full test guide for the turbo linked below. It's important to test at the DME connector (and KLR connector on the turbo) to make sure the signals are making their way to the computers, as the harness is as likely to be a problem as the sensor itself.

https://www.carpokes.com/viewtopic.php?t=525

[BennSport]

I Have an early 1983 model. I tested at the tps itself and wasn’t getting any resistance readings past zero when it was configured to test at idle and WOT. Should I adjust the sensor and see if that makes any changes?

[Tom]

I Have an early 1983 model. I tested at the tps itself and wasn’t getting any resistance readings past zero when it was configured to test at idle and WOT. Should I adjust the sensor and see if that makes any changes?

Not sure I follow your testing. At idle, one of the outer contacts should have continuity to the middle contact (ground) -- i.e., you'll see almost no resistance (like an ohm or two) when the TPS is in the idle position. When the TPS is not in the idle position, you'll see an open circuit with no connectivity between those two pins. In other words, it's a switch that connects at idle and opens when not at idle. When the TPS is in the WOT position, you'll see the same pattern between the middle pin/ground and the other outer pin -- it is also a switch that is either closed at WOT or open whenever not at WOT. If in doubt, take the PTS off the throttle body and test it on a bench -- that will rule out adjustment issues.

[BennSport]

Ah I see what you mean, I should’ve been checking continuity rather than resistance! I was following the write-up on Clark’s garage to see if it was adjusted improperly.

[walfreyydo]

Testing:
https://www.clarks-garage.com/shop-manual/fuel-06.htm

TPS has 3 modes (8v NA): idle, part throttle, wide open throttle (corresponds with the three fuel maps in the DME)

[BennSport]

Inspecting the TPS more closely I found out it’s not even the same part that should’ve came in the car, so I will order the correct one and see what happens then.

[Tom]

What part was it? I'm surprised anything else even fit....

[BennSport]

It was a Bosch 0 280 120301 TPS. My parts catalog calls for a PN: 944 606 113 01 which doesn’t seem to match regarding the Bosch part number.

[Tom]

It was a Bosch 0 280 120301 TPS. My parts catalog calls for a PN: 944 606 113 01 which doesn’t seem to match regarding the Bosch part number.

I think that's the BWM TPS that some people were using on the 944 n/a so save money. People claim it works, but I can't vouch for it personally. Should be easy enough to test -- idle circuit should close when the throttle is shut; WOT circuit should close when throttle is all the way open.