Possible Cause & Correction

Check following items:

• Check for proper valve timing.
• Check for engine vacuum leaks and/or engine not tuned to specifications.
• Check secondary air injection system.
• Check EGR valve for leaking base gasket or valve hanging open.
• Check engine for sticking or leaking valves.
• Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.
• Check fuel injectors. Perform INJECTOR BALANCE TEST in SYSTEM/COMPONENT TESTS article.
• Check fuel system. Perform BASIC FUEL SYSTEM CHECKS in BASIC TESTING article.
• Using Spark Tester (ST-125), check available output voltage of ignition coil.
• Check for crossfire between spark plugs, distributor cap and spark plug wires.
• Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of distributor cap, rotor and spark plug wires.
• Check for an intermittent ignition system problem.
• Check intake and exhaust manifold passages for casting flash.
• Check distributor vent system (if equipped).
• Check harmonic balancer interrupter rings for missing, broken or bent vanes.