What year is your 202? My car does a very similar thing but only once a day. In the morning I drive 2.5 miles to work (lucky me). At the light in front of my office, every time, almost without fail, after sitting there for a few seconds the RPM willdrop momentarily to below 500 RPM and then will level out again and that is the end of it. Considering the car has an air pump and EGR system I have been assuming that this is something to do with the emmissions control system turning on once the car has warmed up a certain amount. This is just a guess of course. But with all the computer decision making going on in this car I have started to call it HAL.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra