Surges Or CHUGGLES

Engine power may vary at cruising speed, or under steady throttle without moving the accelerator pedal. Use a Scan tester to ensure Vehicle Speed Sensor (VSS) signal matches vehicle speed. See VEHICLE SPEED SENSOR (VSS) under ENGINE SENSORS & SWITCHES in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Check the following items:

• Ensure EGR system is okay at idle. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
• Ensure ignition system output is correct.
• Check fuel filter for dirt or restrictions.
• Ensure fuel pressure is correct.
• Check vacuum hoses.
• Check ECM ground contact on engine.
• Ensure alternator output voltage is 9-16 volts.
• Ensure TCC operation is correct. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
• Check O2 sensor for silicone contamination from fuel or incorrect silicone sealant. Sensor may have a White-powdery coating and signal a false rich mixture signal voltage. This signal will cause ECM to reduce fuel, causing lean mixture and driveability problems.
• Remove spark plugs and check for cracks, wear, incorrect gap or heavy deposits.