Once in a great while (and very randomly), my 1993 190 2.6 (77k miles) will idle high. Usually it occurs when I hop errands and am re-starting the car, where the idle will run up to 2200rpm and stay there until I punch the go pedal a little and it will settle back to 750 or so (normal). Today, I got my car washed, drove it the remaining 1/2 mile to work and when I arrived and put it in park, the idle raced up to 1700-or-so rpm. A few jabs at the gas never brought it below 1200 and it stayed at 2100-2200 without falling (or re-setting itself). What gives?