Possible Cause & Correction

Check following items:

• Check for proper valve timing.
• Check for engine vacuum leaks and/or engine not tuned to specifications.
• Check for faulty air injection divert valve or check valve.
• Check for electric air switching valve or electric air divert valve not switching air pump discharge to air cleaner/atmosphere during engine starting or deceleration.
• 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.
• Using Spark Tester (ST-125), check available output voltage of ignition coil.
• Check for crossfire between spark plugs, distributor cap and spark plug wires.
• Check for an intermittent ignition system problem.
• Ensure initial ignition timing is properly set.
• Check intake and exhaust manifold passages for casting flash.
• Check harmonic balancer interrupter rings for missing, broken or bent vanes.