1999 Mercury Sable transmission problem. Torque converter clutch locked up solid. Runs great in neutral and park. Put it in gear and it dies down and surges to try to keep from stalling. Occasionally stalls at stop signs. Goes down the road fine but will not free-wheel and idle dips back down and lugs on the transmission when stopped.

SOURCE: engine stalls at stop lights and stop signs

sounds like the torque converter lock up might not be disengaging. You might also want to check for engine vacuum leaks. Does engine idle smoothly when in park or nuetral ? if the idle is good I would suspect torque converter problem.

SOURCE: 1994 Nissan 3.0 pickup surges

check error codes
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SOURCE: corsica stalls at stop signs

sounds like the EGR valve is sticky, take a small screw driver and tap the valve when the engine is at idle and you will notice a change in the way the engine runs, if the vehicle smooths out disconnect the valve and drive the vehicle and it should not cut off please let me know and dont forget to rate me!!

SOURCE: engine stalls when put into gear, idle fines in park

This is a comon problem with GM cars.Most likely cause is the torqe converter clutch lock up solenoid.

SOURCE: My 1999 grand prix stalls and dies at stops.

My Pontiac Grand Prix is also a 99, it has 216,+ thousand miles on it, it runs great, idles good, I need to replace the oxygen sensor tho as it shuts off on me while driving or sometimes coming to a stop. You might try checking the fuel filter and pump as well.