Throttle Position Sensor: Adjustments

Fig. 65 ISC motor jumper wire:

Fig. 66 ISC motor jumper wire connections:

Fig. 67 TPS test point:

MINIMUM AIR, THROTTLE POSITION SENSOR (TPS) & IDLE SPEED CONTROL (ISC) MOTOR, ADJUST

1. Enter diagnostics and record all trouble codes displayed. Diagnose any trouble codes by referring to appropriate diagnostic procedures before continuing to step 2.
2. Perform ECM input tests. Diagnose any inputs that do not cycle by referring to appropriate diagnostic procedures before continuing to step 3.
3. Verify ignition timing as described under ``Set Timing Mode.''
4. Perform ``DEFI System Performance Diagnosis'' as previously described.
5. Remove air cleaner assembly and plug Thermactor vacuum port.
6. Start engine, then enter diagnostics and select ECM data display ED04. Operate engine until display indicates coolant temperature greater than 85° C.
7. Retract ISC motor until throttle lever is just clear of ISC plunger by applying external power with tester tool No. J-34025 or equivalent or by using jumper harness procedure as follows:
a. Disconnect ISC electrical connector and connect jumper harness to ISC, Figs. 65 and 66.
b. Connect jumper wire between ISC terminal C and 12 volt power source.
c. Apply finger pressure to ISC plunger to close throttle switch, then connect jumper between ISC terminal D and ground until plunger retracts fully and stops. Remove ground wire immediately after plunger retracts and stops to avoid damaging the motor. Also, it is important to apply pressure to plunger when retracting to prevent clashing and binding of the internal gears.
8. With ISC plunger fully retracted, ensure plunger does not contact throttle lever. If contact is noted, turn plunger in with pliers until it no longer contacts lever. Ensure throttle lever is resting on minimum air screw and is not restricted by throttle, cruise or TV cables.
9. Extend ISC plunger by connecting ISC terminal D to 12 volt power source and terminal C to ground.
10. Locate and ground alternator green test connector near the alternator four-way connector. Alternator operation will cease and the ``No Charge'' indicator lamp will illuminate.
11. Check minimum idle speed. If speed is 475-550 RPM, proceed to step 12. If speed is not within specifications, it should be adjusted as follows:
a. If minimum idle speed exceeds 550 RPM, check for vacuum leaks at throttle body, intake manifold, vacuum fittings and hoses and correct as necessary before performing adjustment.
b. Ensure alternator is not operating and ``No Charge'' indicator is illuminated.
c. Adjust minimum idle speed to 525 RPM by turning the minimum idle screw as necessary.
12. Stop engine and turn ignition key to the On position. Open throttle fully, then let it snap shut against the throttle stop screw. Select ECM data display ED01 and note value. If throttle angle reading is -1.0-+1.0, proceed to step 13. If reading is not within specifications, the TPS should be adjusted as follows:
a. Connect a suitable voltmeter to TPS test point, Fig. 67. With meter set on the two volt scale, backprobe test point with meter positive lead connected to pin A (circuit 417) and negative lead connected to pin B (circuit 476).
b. If TPS voltage measures 0.45 - 0.55 volt, no adjustment is necessary. Proceed to step 13.
c. If voltage reading is not within specifications, loosen TPS screws just enough to allow rotation of the sensor, then open throttle and allow throttle lever to snap shut against minimum air screw. Rotate sensor until voltmeter indicates .50 volt, then tighten attaching screws and recheck adjustment. Do not use excessive force when adjusting the TPS.
13. With engine off and ignition key in the On position, fully extend ISC motor plunger as described in step 9. It may be necessary to apply and release the ground several times to move the ISC plunger from its retracted position.
14. Apply and release power to extend ISC plunger while observing a voltmeter connected at the TPS test point.
15. Backprobe TPS test point with positive meter lead connected to pin A (circuit 417) and negative lead connected to pin B (circuit 476). With meter set to two volt scale, apply and release voltage several times and note voltmeter value with ISC stopped. At full extension of the ISC, one of two values should be observed; a high value at top of ratchet and a low value at bottom of ratchet. Stop the ISC when the highest voltage is observed.
16. The highest TPS voltage should be 1.05-1.10 volt. If voltage is not within specifications, adjust the plunger in or out as necessary, then recheck maximum voltage.
17. Disconnect all test equipment and reconnect ISC connector. Turn ignition key off for a minimum of ten seconds, then start engine and check ISC motor for proper operation.
18. Remove ground from generator test lead, then reinstall air cleaner assembly and reconnect vacuum hoses. It is possible that the above adjustments may illuminate a telltale light or set a trouble code. In this event, diagnostics should be entered and stored codes cleared.