Engine revs up/down on its own

[jondee86]

El_Camino Wrote:The car revs in idle cold/warm between 1500-2000 RPM.
Even worse, after hard driving its revving between 2000-3500

The 1500-2000 rpm lope is usually the engine cycling on fuel cut, and the
typical cause is a non-functioning thermostatic idle-up valve. You can test
for that one as fax has outlined above.

The 2000-3500 rpm lope is a bit more interesting :E Theoretically. with a
closed throttle and high manifold vacuum, fuel cut will be initiated if the
engine speed is above 1700 rpm, and fuel will be restored when the engine
speed drops to 1400 rpm... +/- a couple of hundred rpm to allow for
gauge error and overshoot.

Does the hot engine rpm actually lope (move up and down by itself) or
does it just hold steady at some rpm between 2000-3500 rpm ?

Cheers... jondee86