[alloro]

A yellow spark at the end of a spark plug is a sign of a weak spark, it should be blue. The plug wires, cap and rotor, pick-up coil in the distributer, crank sensor, and ignition coil are the primary suspects for a weak spark. Check the spark color using the wire that comes directly off the coil. If it's still yellow then you've eliminated the wires, cap and rotor as possibilities. If however the color is blue, then one of those items is the problem.