1990 Volvo 240

Engine Performance problem
1990 Volvo 240 4 cyl Two Wheel Drive Automatic

after starting the car, the idle picks up, then progressively gets to a point and levels off I could drive the the car on level road at 35 or 40 miles per hour, but if I drive with overdrive off the idle speed will drop slightly and return depending on the grade of the road, it was fine for one hour yesterday then returned.
Arthur koch
July 2, 2010.

Have these components checked out idle speed solenoid, throttle position sensor and throttle position switch

Jul 2, 2010.