TPS ADJUSTMENT
Difficulty? Easy
Total time: Minutes!
Applications: 86-88 NA/Turbo, 89-91 NA/Turbo
DISCUSSION:
The Throttle position sensor. AKA: The TPS!
The TPS is the black plunger in the center. The screw in front of the TPS is used to make adjustments.
The TPS is part of the Fuel and Emission Control System. It has two major functions: To cut the fuel off when you snap the throttle shut from wide open throttle. (This prevents backfires...) And the sensor also tells the ECU the position of the throttle body. This allows the ECU to make adjustments to the air/fuel mix at different throttle positions.
Most common signs of a bad TPS is a car that runs rough at Idle or a car that has a hesitation problem during acceleration. Bad backfiring could also be a 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 have a single piston TPS, the 89-91 cars have a dual piston TPS. The 86-88 sensor is not inter changeable with the 89-91. However they are adjusted exactly the same!
Diagnostics:
STEP 1) First test would be warm the car up, hold the throttle body open at about 2,000 RPM and move the TPS with your finger. This will cause the engine to rev faster and slower. This test verifies 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 you need to start checking connections.
STEP 2) Check the resistance values with an Ohm meter. (These values are from the 86-88 Mazda shop manual, they may be different for 89-91 cars) Disconnect the plug from the TPS sensor itself. Hold the plug with the single electrode on top, and the two electrodes at the bottom. Connect the Ohm meter to the top electrode and the bottom right electrode.
At idle you should see ~ 1k Ohm
At WOT ~ 4-6K Ohm.
If not, then replace your TPS.
STEP 3) If the TPS appears to work from the first step, then you can continue to check the TPS adjustment. Now before I continue, I have to acknowledge the two ways of adjusting the TPS:
One is by using test lamps, the other is by using two volt meters. Some RX7 owners believe that using the volt meter setup is more accurate, but I disagree... Why? Simple: When you use the volt meter method your setting the TPS according to the numbers you see on the volt meter. This gives you a very accurate reading of the signal coming out of the TPS sensor, but it does not tell you what the car sees at the ECU...
The test lamp method uses the signal sent FROM the ECU to the test connector. This method in my own words is more accurate because you are adjusting the TPS according to what the ECU sees and I think the ECU knows more about what the proper signal should be, more than two volt meters. 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. I got my LED's at radio shack for about 3 bucks. The spade connectors you need are 1/4". The LED's that you buy should come pre-wired each with a black and red wire. (They should be 12 volt ones.) All you do is tie the two red wires together and put a spade on the end. Then put a spade on each of the black 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:
Its the little green connector in the center.
Insert the red spade into the top and the black ones into the bottom two.
Before you do this test, make sure the car is warm!!!
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. (The Mazda Manual picture...)
And that is it. The hardest part is building the test lamps... Some people use regular light bulbs, but if you use LED lamps you can actually save the test lamp assembly to pull error codes from the ECU!!! (86-88 only) Very useful since the dealer wants $75 just to check error codes! More on that in the ECU section...