this is spooky

92 jimmy 4.3l- w -

a few times over the past few weeks i go out and start it up - while im sitting there foot off the gas pedal - the engine revs up to about 1500 alonng with the speedometer ( digital) - vss checked out ok by gm . ??

"Sitting" as in "not moving?" If the idle RPM is flaring whiel in PARK or NEUTRAL it may be that the PCM is increasing IAC counts due to a cooling fan anticipate, A/C compressor anticiapate, or the CS signal is going intermittent (but still within the allowable range) and the PCM is adjusting target idle based upon that input.

Another remote possibility would be internal vacum leaks from a brake booster, EGR, or PCV system, or a TPS signal that is intermittent.