TPS & SAS Idle Speed System

Two procedures in the source: DOHC Turbo (our truck’s configuration) on printed p.134, and SOHC on printed p.135. Both adjust idle speed via the SAS (Speed Adjustment Screw) and verify the Throttle Position Sensor (TPS) output.

DOHC Turbo procedure (printed p.134)

1. Remove the TPS connector and inspect pins for corrosion. Clean as required.
2. Use a feeler/thickness gauge to set the SAS lever gap. Loosen the SAS (Speed Adjustment Screw) as shown, then set the gap.
   • SAS gap limit: 0.55 mm (0.022 in)
3. To adjust TPS position, loosen the TPS attachment screws as shown.
4. Attach jumper lead MB991536 to Connector #2, Output Pin #4 (-), as shown. Connect a voltage meter.
5. Turn the ignition switch to ON (not start).
   • Output voltage limit: 580-690 mV

Notes: see the TPS code chart for detailed readings. Check harness ohm range (see Diagnostic Harness Pin Guide) before replacing the TPS unit. TPS internal components cannot be adjusted — replace out-of-range units, do not attempt internal repair.

SOHC procedure (printed p.135)

1. Loosen the SAS (Speed Adjustment Screw) locknut as shown. Do not turn the screw itself at this point. Attach the RPM test unit to the RPM engine harness connector as shown.
2. Start the engine and verify RPM settings.
   • RPM setting: 850±50 — (verify printed p.135): this conflicts with Data & Specifications (printed p.121), which lists SOHC idle speed as 800±50 rpm and DOHC as 850±50 rpm. This page’s SOHC procedure states the same 850±50 figure given elsewhere for DOHC. Do not adjust idle speed on a SOHC vehicle to 850 rpm without resolving this discrepancy against a clean scan of both p.121 and p.135.
3. The SAS screw cannot be turned more than 1/2 turn in either direction from its set position. Do not exceed this limit. Tighten the locknut when the test is complete.
4. If idle settings are correct, verify the TPS unit: remove the TPS connector and inspect pins for corrosion, cleaning as required.
5. Attach jumper lead MB991536 (PWR output / Ground (-) as shown). Connect a voltage meter.
6. Turn the ignition switch to ON (not start).
   • Output voltage limit: 580-690 mV

Notes: see the TPS code chart for detailed readings. Check harness ohm range before replacing the TPS unit. TPS internal components cannot be adjusted — replace out-of-range units, do not attempt internal repair.