Possible Cause & Correction

Inspect for loose wiring grounds at engine block. Check ignition system for faulty components. Check for crossfire between spark plugs (plugs, distributor cap and proper wire routing). Check ignition timing.
Inspect distributor for worn components. Ensure AIR system is pumping air into the exhaust manifolds at all times. See CHART C6 - AIR MANAGEMENT DIAGNOSIS. Refer to the DFI SYS/COMPONENT TESTS article in this section.
Check intake manifold bolts for tightness. Check for worn or damaged distributor or internal engine components.