Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1989STEP VAN P30, 7.4 W, AUTOMATIC, 475/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCEADJUSTMENTTUNE-UP - V8ADJUSTMENTSCONTROLLED IDLE SPEED CHECKTHROTTLE BODY INJECTED ENGINES
1989 Chevrolet Step Van P30, 7.4 W, Automatic, 475/M40
Throttle Body Injected Engines
1989 Chevrolet Step Van P30, 7.4 W, Automatic, 475/M40SECTION Throttle Body Injected Engines
- Ensure no codes are displayed, idle air control system has been checked, and ignition timing is correct. See IDLE AIR CONTROL (IAC) SYSTEM CHECK chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
- Set parking brake and block drive wheels. Connect "SCAN" tester to ALDL connector with engine in open loop. Start engine and warm to normal operating temperature. Place transmission in Drive (auto. trans.) or Neutral (man. trans.).
- Check "SCAN" tester for correct position of Park/Neutral switch. Check controlled idle speed and IAC valve pintle position counts. See CONTROLLED IDLE SPEED (RPM) table. If within specification, idle speed is being correctly controlled by ECM.
- If not within specification, go to "ROUGH, UNSTABLE OR INCORRECT IDLE; STALLING" TROUBLE SHOOTING in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
CONTROLLED IDLE SPEED (RPM) (1)
| Application | Man. Trans. | Auto. Trans. | |||||
|---|---|---|---|---|---|---|---|
| 5.0L | 600 | (2) 500 | |||||
| 5.7L | |||||||
| Under 8500 GVW | 600 | 525 | |||||
| Over 8500 GVW | 600 | 550 | |||||
| 7.4L | 800 | 750 | |||||
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.