2nd Gen TPS Adjustment

Adjustment tips for the Throttle Position Sensor(s) (TPS) on a 2nd Gen RX-7 (mine is a 1990, if yours is a 86-88, or a turbo, details may differ slightly.)

DISCLAIMER

If you screw it up, its not my problem. Only competent mechanics should attempt this adjustment. Engines are dangerous. Running engines and dangling multi-tester leads are even more dangerous.

Warnings

There are two methods, the FACTORY method, and the JOHNR VOLTMETER method. Both methods assume you have a (digital or high-quality) voltmeter. Never, never, NEVER, use a +12v "test light" on a test connector. These pull lots of current and will fry the engine computer!

Two Adjustment Methods

Factory Method

Buy a Mazda Factory Service Manual from HELM. They can be reached at 1-800-782-4356. (Or try Mazdatrix) See the Fuel section (F1 for NA, F2 for turbo). In the back of the section, there is a 1/2 page on checking and adjusting the TPS. I expand on that section here.

Warm up the engine to proper operating temperature
Stop the engine and remove the key.
Ground the "Test/check connector" if you can find it. Don't sweat it too much if you cannot find it, I don't think it makes a difference.
Insert the key and turn to the ignition position. (Do NOT start.)
Find the green 3-pin connector between the intake air filter box, and the right front strut tower.
It should look roughly like this:
--------- | A | B | --------- \ C / -----C is "hot" or positive. A and B are (switched) ground. Hook your tester up with the positive lead in C. Only one side (A or B) should get to 12V. If both A and B read 12V, or if neither do, you've got some adjusting to do...
Adjusting... - Find the slotted screw (also has a locking nut on the back, and very fine threads) on the TPS. The TPS is located in the front, center of the intake plenium. It is right smack in the middle of the engine compartment, right in front of the intake. (Kinda sticking its tongue out at you.) There are two small black round "plungers" mounted on it. The one closest to the front is the NARROW range sensor. If you turn the throttle you'll notice it is completely extended at less than 1/2 throttle. Then one in the back is the FULL range sensor. This one measures the entire throttle range.
Once you have found the parts, you begin playing a simple game. The game is to try to get only one socket (a/b) to be "active", with the other one dead. If you turn the screw and listen for clicks, you can also tell when you've passed a threshold. Hook the meter up to one of the sockets and turn the screw 1-2 turns. If nothing happened, try the other socket. Something should have changed. (They probably went from both off to both on, or vice-versa.) There is only about 1/2 turn of "usable" range where only 1 side will be active. I usually find this range, then "blip" the accel a few times to make sure the throttle has really settled. Keep repeating this process, turn, blip, measure both sides - until you are satisfied you have found the "center".
Chances are it took you so long to figure this out the engine got cold. Take another test drive, and see if there is an improvement.
ALWAYS do a final test (step 7) again once you are back from the test drive. The hotter engine will change the tolerances of the TPS, and you want then set with a warm/hot engine.

JohnR Voltmeter Method.

Use a DIGITAL VOLTMETER with a high input impedance ONLY. No Cheapos. If you short things, it is possible that you could fry your ECU. (See DISCLAIMER above.)