I have a 1994 Ford Taurus, 190K miles, 3.0L engine. It runs fine, but
when I start the engine, it goes into a rhythmic behavior while idled.
The engine will start to wind down, almost as if it is going to stop,
then it will rev back up again, only to slow down. It does this
continually without ever quite shutting off. As soon as I put the car in
drive or reverse, the behavior quits and the engine performs normally.
The pulse is about 2 seconds in each direction. Does anyone have any
idea what this is and what it means?