Possible Causes & Corrections
Check the following items:
- Ensure vehicle operator is using the correct starting procedure.
- Monitor Engine Coolant Temperature (ECT) sensor with scan tool. Compare engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit.
- Check Throttle Position (TP) sensor. If a sticking throttle shaft or binding linkage causes a high TP sensor voltage or an open throttle indication, the control module will not control the idle. While monitoring the TP sensor voltage, the scan tool should display less than 0.85 volt with throttle closed.
- Inspect fuel pump relay for proper operation. The fuel pump should operate for the first 2 seconds after turning ignition on. See Fuel Pump Electrical Circuit Diagnosis in FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
- Check fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
- Inspect for water contamination in fuel.
- Perform fuel injector coil test. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
- Perform fuel injector balance test. See SYSTEM & COMPONENT TESTING - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
- Inspect fuel pump check valve.
- Check for proper ignition voltage output with a Spark Tester (J-26792).
- Inspect spark plugs. Check for wet fouling, cracks, wear, improper gap, burned electrodes or heavy deposits.
- Check for bare or shorted ignition wires.
- Check for moisture in the distributor cap, if applicable.
- Inspect loose ignition coil connections.
- Inspect loose ignition control module connections.
- Inspect faulty control module or ignition system grounds.
- Improper valve timing.
- Low compression.
- Bent pushrods.
- Worn rocker arms.
- Broken or weak valve springs.
- Worn camshaft lobes.
- Check intake and exhaust manifolds for casting flash.
- Check Idle Air Control (IAC) operation. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
- Inspect for a restricted exhaust. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.