If you experience difficulty starting the engine when cold, stalling at idle, or hesitations during acceleration, it may be the idle air bypass valve. This valve helps the vehicle idle steady when the accelerator pedal is not pressed.Google+
Car Problem Reports
Ford Thunderbird SC Problem With Idle Air Bypass Valve May Cause Engine Performance Problems
Ford Thunderbird SC Problem
Model Year Affected: 1990
Average Mileage: 105,410 mi (68,230 mi - 125,000 mi)
Visitor, 1990 Ford Thunderbird SC, 68,230 mi
Same problem here. Trouble starting, stalling out when idle directly after starting, and hesitation when accelerating. Replacing the idle air bypass valve fixed it all.
Visitor, 1990 Ford Thunderbird SC, 125,000 mi
When engine is cold, starts fine but when partially through warm-up cycle engine at idle lugs and stalls. no apparent reason for failure. RPM while shifting is erratic as well as base idle level is low.
Visitor, 1990 Ford Thunderbird SC, 123,000 mi
when i put the car in drive and i am at a stop light or something were the car is not moving it idles to were there is a small viberation and i cannot figure out what it is motor mounts are fine i replaced the map sencor and the idle control sencor but still problem is accuring