Introduction

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The Throttle Position Sensor (TPS) is part of the Fuel and Emission Control System. It has two major functions: turns injectors off on deceleration to prevent fuel loading which will cause the engine to buck around during deceleration, and to tell the ECU the position of the throttle opening. This allows the ECU to make adjustments to the air/fuel mix at different throttle positions.

The most common signs of a bad TPS are, rough or bouncy idle and hesitation during acceleration. Bad backfiring can also mean bad TPS, but backfiring is usually caused by having an aftermarket free flow exhaust.

NOTE: There are two types of throttle position sensors. The 86-88 cars use a single throttle sensor while the 89-91 cars use 2 throttle sensors as a single assembly. The 86-88 throttle sensor assembly is not interchangeable with the 89-91. However they are adjusted exactly the same!

Diagnostics

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Note: Warm up the engine if you still have the thermowax on the throttle body before performing this test!

STEP 1) Warm the car up, hold the engine at about 2,000 RPM, and move the TPS with your finger. This should cause the engine to rev faster and slower, verifying that the signal from the TPS is making it to the ECU, and that the ECU is interpreting the signal properly. If it doesn't affect the engine speed, start checking connections.

STEP 2) Check the resistance values with an Ohm meter. Disconnect the TPS plug, refer to the image and resistance values below. Also check for a smooth resistance increase and decrease in between idle and WOT plunger positions, though your digital multi-meter (DMM) may hesitate as its range changes.



S4 TPS Resistance Check
A to B

• Idle: 0.90 - 1k
• WOT: 4k to 6k

A to C

• Idle: 4k to 6k
• WOT: 2k to 3k

S5 TPS Resistance Check
A to B

• Idle: 0.8k to 1.2k
• WOT: 4k to 6k

E to D

• Idle: 0.6k to 0.9k
• WOT: 3.4k to 5.1k

STEP 3) If the TPS appears to work from the first step, continue to check the TPS adjustment. The two primary methods of adjusting the TPS are using test lamps and using volt meters. The test lamp method is preferred because it uses the signal sent from the ECU to the test connector, allowing you to adjust the TPS according to what the ECU sees. The test lamp method is also the method used in the Mazda factory manual.

To set the TPS using the test lamps you need two things: Two LED's and a couple of spade connectors. Radio Shack carries 12V LEDs and the 1/4" spade connectors. All you do is tie the two red LED wires together and put a spade on the end, then put a spade on each of the black LED wires. Done!

To hook it up to the car, find the diagnostic connector right by the air filter and boost sensor. Its a three wire green plug like this:




Insert the red spade into the top and the black ones into the bottom two. Next step is to turn the car ignition on. Check your test lamps: You can either have one lamp on, both on, or neither on. If one lamp is one, that's good! If neither or both is on, you need to turn the TPS adjusting screw until you can get only one lamp lit at a time.



You can save this test lamp assembly and use it for [Tapping into the S4 Diagnostics Plug] or [Tapping into the S5 Diagnostics Plug].

Other Methods

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See Also...

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• [Idle System Overview]
• [Idle Troubleshooting]
• [Tapping into the S4 Diagnostics Plug]
• [Tapping into the S5 Diagnostics Plug]