Hi guys,
I've had the throttle body off a few times for various reasons and I thought I'd share with you my procedure for calibrating the TPS. As SergAnt and other gurus will tell you it's important that the TPS is calibrated correctly otherwise engine power and fuel consumption can be adversely affected.
This is one of the reasons that I invested in a chinese Tech2. With this baby you can run a throttle position sensor test where you can step through all the throttle positions from 0 through to 10 and display the TPS voltage.
The adjustment procedure that I recommend is as follows:
1. Remove intercooler cover.
2. Loosen the clamps on the pressure hose between the intercooler and the throttle body.
3. Remove the intercooler mounting bolts. No need to remove all four, just the two on the throttle body side will suffice.
4. Remove the pressure hose between the intercooler and the throttle body.
5. Remove the intercooler bracket that is attached to the throttle body.
6. Remove throttle body assembly, take off stepper motor and TPS. Make sure that you don't lose the small section O-ring that seals the TPS to the throttle body.
7. Clean the throttle body with good quality carby cleaner. It's important that you take the stepper motor and TPS off before you use the carby cleaner as it's an aggressive cleaning agent and could easily damage them.
8. After cleaning, and before reinstalling the stepper motor and TPS, ensure that the throttle blade moves freely throughout its entire travel without binding and that the return spring moves the blade back to wide open without hesitation.
9. Clean the O-rings that seal the stepper motor and TPS with a clean lint free rag then mount the stepper motor and TPS back on the throttle body. Nip the mounting screws up just a bit but leave them loose enough so that you can rotate the stepper motor and TPS against the throttle body.
10. Loosen the jam nut on the small allen head screw which determines the maximum blade angle and loosen the screw. This needs to be loosen to ensure that the stepper can move the throttle blade to its maximum extent.
11. While I've found that you can adjust the TPS with the throttle body installed on the manifold, it's much easier to adjust everything with the throttle body connected but just sitting on the manifold as shown in this image
12. Disconnect the glow plug wiring harness as shown. This will reduce battery drain while you adjust the stepper motor and TPS positions.
13. Turn on the ignition without engaging the starter, power up the Tech2, go to the Miscellaneous Test menu and select Throttle Position Motor.
14. Scroll down the data display until you see TPS voltage above the Throttle Position at the bottom of the display.
15. Use the ‘Decrease’ soft key to get the stepper motor to zero steps if it isn’t already there then rotate the TPS until the TPS voltage is as close to 0.50V as you can get. The allowable voltage range is 0.44V to 0.56V.
16. Tighten the TPS mounting screws and ensure that the TPS voltage has not changed.
17. Use the ‘Increase’ soft key to advance the stepper motor to 1 step, then rotate the stepper motor until the TPS voltage is as close to 0.84V as you can get. The allowable voltage range is 0.75V to 0.95V.
18. Go through all the stepper motor positions and record the TPS voltage for each step. The allowable voltage values are in the table below.
19. Repeat step 18 a number of times to see if the TPS voltage remains the same each time. Note that the allowable voltage variation is by +/- 0.02V between runs.
20. With the stepper motor at step 1, tighten the stepper motor mounting screws and ensure that the TPS voltage doesn't change.
21. Select zero steps, unscrew the allen head screw then push the throttle blade until it contacts the throttle body. Next, screw in the allen head screw until the throttle bade starts to move away from the throttle body. Note the voltage on the Tech2 - it should be higher than was achieved at 10 steps.
22. Retighten the jam nut and recheck that the TPS voltage at 10 steps has not changed.
23. Power off the Tech2 and turn off the ignition.
24. Disconnect the stepper motor and TPS wiring and reinstall the throttle body using new gaskets.
25. Reconnect the stepper motor and TPS wiring.
26. Reinstall the intercooler bracket that bolts to the throttle body.
27. Reinstall the pressure hose between the intercooler and the throttle body.
28. Tighten the intercooler mounting bolts.
29. Tighten the clamps on the pressure hose between the intercooler and the throttle body.
30. Replace intercooler cover.
31. Reconnect the glow plug wiring.
32. Start the engine and re-run the Throttle Position Motor test on the Tech2 as a final confirmation.
Edit #1: forgot to mention to retighten the stepper motor and TPS mounting screws!
Edit #2: Changed the procedure for adjusting the allen head screw. Since my OP I have observed via the Tech2 that, when shutting down the engine, the ECU commands to stepper motor to step 11, which I presume is to fully close the air intake to gently stop the engine.