My friend always suspects the plug wires first in this situation, and then the
cap and rotor.  Check these out (simple and easy to do) first and if they are
OK (no thin spots in the insulation of the wires, no moisture in the cap, no
burnt towers in the cap or carbon tracks.  Clean the cap with alcohol if there
are carbon tracks) then we can move forward in our troubleshooting.
Ken Wilford
Van-Again
John 3:16