Possible Cause & Correction

Compare vehicle to another vehicle of similar design. Ensure vehicle has actual problem. Remove air cleaner and replace filter if dirty or plugged. Check the following if problem still exists:

• Ignition timing.
• Restricted fuel filter, contaminated fuel, or improper fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
• ECM grounds.
• EGR operation to ensure EGR valve is not open (or part open) all the time. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
• Alternator output. Repair if less than 9 volts or more than 16 volts.
• Valve timing. Perform compression test.
• Proper or worn camshaft.
• Exhaust system for restriction:
• With engine at normal operating temperature, connect vacuum gauge to convenient intake manifold vacuum port.
• Disconnect EGR solenoid electrical connector, or connect EGR valve directly to vacuum source (by-passing switches and/or solenoids).
• Run engine at 1000 RPM and record vacuum reading.
• Slowly increase speed to 1500 RPM and note vacuum reading at steady 2500 RPM.
• If vacuum at 2500 RPM decreases more than 3 in. Hg from reading at 1000 RPM, inspect exhaust system for restrictions.
• Disconnect exhaust pipe from engine and repeat previous 2 steps. If vacuum still drops more than 3 in. Hg with exhaust disconnected, check valve timing.