ruling out a sensor because another nearly identical car does the same thing is an excellent way of isolating a problem - unless you are talking about the darn temp sensors. My climate control comes on too early and the sensor to control the aux fan is screwy too. It does whatever it d*** well pleases. All I'm saying is, your diagnosis procedure makes sense except these sensors seem to be fairly problematic when they get old. Mine are.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.