Mine was the mass air flow sensor twice in 360K! 93 300E, 3.2L what a car!!! Occasionally a bad MAF will act up if you tap on it by hand. Unfortunately it usually takes a known good replacement to rule it out. As for the harness, remove some of the protective sheathing in various locations. If it is bad it will have crumbling insulation underneath.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer