Short answer
Check the mounting holes first. Round holes mean the sensor is fixed: it reads correctly when installed, and a wrong reading means a wrong part, a bad sensor or a wiring fault. Slotted holes mean it can be adjusted: key on, engine off, back-probe the signal, loosen the screws, rotate the sensor until the closed-throttle voltage matches the factory spec in your service manual, tighten, and recheck.
Is your TPS adjustable?
How to tell from the mounting holes
| What you see | What it means |
|---|---|
| Slotted, curved mounting holes | Adjustable. Set it to the factory voltage. |
| Round mounting holes | Fixed. Not meant to be adjusted. |
| No separate sensor; motor housing on the throttle body | Electronic throttle. The sensors are internal and not adjustable. |
BBK’s instructions for 1985 to 1997 GM Tuned Port and LT1 throttle bodies note that "Tuned Port sensors are factory slotted," and tell installers to check the TPS voltage with a digital voltmeter and adjust it to the factory specification. BBK’s instructions (PDF) show the slotted holes in a diagram. That is the classic adjustable design. By contrast, an SMP listing says its sensors are built to match OE output rather than using adjustable designs.
How to adjust a TPS sensor
Make sure the throttle is fully closed
The throttle stop should rest against its screw with no cable tension holding it open. Do not move the throttle stop screw to fix a TPS reading; that changes base idle.
Connect the meter
Key on, engine off. Back-probe the signal wire with the red lead and put the black lead on the sensor ground, or a good ground if your manual says so. Set DC volts.
Loosen the screws
Loosen the two mounting screws just enough that the sensor turns with firm hand pressure.
Rotate to the spec
Turn the sensor slowly while watching the meter until it reads the factory closed-throttle voltage.
Tighten and recheck
Tighten the screws, then read it again; tightening can move it slightly. Then open and close the throttle a few times and check that it returns to the same reading.
Sweep and relearn
Do a slow sweep to confirm a smooth signal, clear codes, and run any relearn your service manual lists.
When adjustment will not fix it
- The sweep has jumps or dropouts: the track is worn. Replace the sensor.
- The reading moves when you wiggle the harness: repair the wiring.
- The sensor will not reach the spec at either end of its slots: wrong part, wrong throttle stop setting, or a worn throttle shaft.
- You have a P2135 on an electronic throttle: there is nothing to adjust. See P2135.
Questions people ask
Can all TPS sensors be adjusted?
No. Many sensors are built to match the original output without adjustment. An SMP listing says its sensors match OE output rather than using adjustable designs. If your sensor has round mounting holes, it is not meant to be adjusted.
What voltage should I set the TPS to?
The factory closed-throttle spec for your engine, from the service manual. Numbers posted in forums vary widely between engines, and setting the wrong one causes idle and shifting problems.
Should I slot the holes on a fixed sensor?
Not on a stock engine. If a correct, working sensor reads out of range, look for a wiring fault, a worn throttle shaft or the wrong part. Performance throttle body makers sometimes call for slotting, as BBK does for some GM Tuned Port bodies, but that is a specific case with its own instructions.
Do I need to relearn after adjusting?
Often, yes. Changing the closed-throttle reading can upset idle until the computer relearns. Follow the relearn in your service manual.
Sources
Last reviewed 2026-10-12. General guidance only: specs, procedures and fitment vary by vehicle, so confirm in your service manual and on the listing before you buy or wrench.