OK, I suppose this makes sense, at least intuitively, that the smoother the idle the higher the vacuum, though I wonder what the mechanism for this is. (So a 1960's muscle car with a lumpy idle due to its camshaft profile would show less vacuum.) I suppose we'd have to average the signal over some time frame, since any very fast pressure sensor in the intake will show a cyclic pattern as the valves open and close. In the example waveform for the WPS it varies over a span of about 1" Hg (converting from psi). You mentioned the WPS500X; would the FirstLook be any different?A good engine running at a smooth idle with no electrical or mechanical defects will return a stable 20"Hg of vacuum.
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