Possible Cause & Correction

WARNING: This page is about a different car, the 1995 Cadillac Seville and 1995 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

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 appropriate SYSTEM/COMPONENT TESTING article in the ENGINE PERFORMANCE section.
SYSTEM/COMPONENT TESTS - 4.6L (for Concours & Seville)
SYSTEM/COMPONENT TESTS - 4.9L (for DeVille only)
Check fuel system. Perform BASIC FUEL SYSTEM CHECKS in BASIC TESTING article in the ENGINE PERFORMANCE section.
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.
Ensure initial ignition timing is correct (4.9L HEI only).
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.