1993 Buick Century, 3.3L. Transmission problem
 

My car is 1993 Buick Century, 3.3L. When I start engine and then try to move, the engine stalls, "serve engine soon" light appears.

The engine error code was 28(gear switch in transaxle).

But after warming up engine for 10-15 min the car goes normally.

The transmission fluid level is normal.

Please help.