What will cause a 1999 Pontiac Bonnieville 3800 V6 that runs good when cold and fans operate normally after it gets hot (200 Degrees) not restart? The operation temp is150 Degree running on highway ,Stop and go traffic temp goes up to 200 Degrees,stall out sometimes.Won't restart after car gets hot 200+degrees.Let car sit and cool down to 150 then starts rough but runs and smothes out .

SOURCE: 1999 Pontiac Firebird 3800 V6 engine

air filter dirty/bad engine ground connection/fuel not reaching injectors/loose connection on ignition system

SOURCE: cooling fans will not operate

IF YOU HAVE A SCANNER, WATCH THE COOLANT TEMP. LET THE ENGINE RUN UNTIL THE FANS COME ON. IF THEY DO. THE SYSTEM IS DESIGNED TO COME ON AT AROUND 228 DEGREES.

SOURCE: once the car gets to op.temp it starts to run rough

I had the same problem with my pontaic gran am se 2.4l.
The small vacuum hose near the fuel filter dry rotted,cause the car to idle and stop at red lights.

SOURCE: i have a 93 firebird

Hi there, have you checked the colour of the oil in the motor, if not clear or normal and have a milky look, it sounds like the head gasket is on the way, it will still drive but the symptoms sound like the head gasket, Check the oil. Hope this will be of some help to solve the problem

SOURCE: 1997 Pontiac Bonneville starting issue: My

First thing to do is replace you fuel filter, If there is a check engine light have the code read, Most parts store will do this for free. Get the code number type that into google for further advise.