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 MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 150 (ENGINE CONTROL SYSTEM - TROUBLE SHOOTING - NO CODES)SYMPTOM DIAGNOSISHARD STARTADDITIONAL CHECKS
1999 GMC Forward Control 5.7 R, Automatic
Additional Checks
1999 GMC Forward Control 5.7 R, AutomaticSECTION Additional Checks
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
- An Idle Air Control (IAC) system that is malfunctioning can cause a hard start condition. Hold throttle open slightly while starting the engine. After vehicle is started, the scan tool can be used to check the IAC valve operation. Operate the IAC valve using the scan tool while checking for a smooth increase and decrease in engine speed. If engine speed can be controlled, IAC system is functioning normally. If engine speed cannot be controlled using the scan tool, refer to DIAGNOSTIC AIDS under DTC P0505: IDLE CONTROL SYSTEM under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 1.8L VIBE article.
- If the engine stalls after starting, check for a fault in the CMP Actuator System or the Rocker Arm Oil Control System. A stuck On control solenoid can cause the engine to stall at idle speeds. See DTC P1346: INTAKE CMP SYSTEM PERFORMANCE and DTC P1692: ROCKER ARM ACTUATOR SYSTEM STUCK ON under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 1.8L VIBE article.
- Check Technical Service Bulletins for any updates.
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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.