car stalls a lot

99 grand am,v-6 SE-2.my car has recently started to stall at times.mostly in the afternoon when it is hotter.runs for about 20 min. and then looses power and stalls.will not restart unless I turn the key off and back on.sometimes I have to do this about 10 times before it stays running.each time I turn it back on the fuel pump pumps up within seconds.stalls at idle and at part throttle.when it starts to stall you can here it sucking air big time.when it runs it runs great.there are no codes.once it starts to stall it never recovers,just takes longer sometimes.any ideas?I am a mechanic with tools,but I am not an automotive mechanic.give me a carburator and a distributer and I'm right at home.I have no knowlege with the new electronics.help

Sounds like your fuel pump is going, especially if it takes 10 or more minutes to restart......could also be a crank sensor.....need to check two things when this happens, spark and fuel pressure....

Keep a can of carb cleaner handy in the car.......when it stalls and won't start, spray the carb cleaner into the intake....wait a few seconds, and spray some more....now try and start the car.....if it starts and runs, and continures to run as long as you spray, then it's probaly lack of fuel pressure.....it's not the PassLock system......that will not cause the car to stall.....in fact, if the system did fail once the car is already started, the SECURITY light will come on and the car continues to run, and the car goes into a failsafe mode, which allows the car to start.....

If you spray the carb cleaner and it doesn't start, check for spark(could be crank sensor, ICM, etc.)......

stalling issue seems to have gone away but idle is rough and I can smell gas in the exhaust.car idles at 650.if I rev to 800 idle is smooth.no skipping or hesitation.service engine soon light is on.I get a misfire code every once in a while.also the p0440 code is active quite a bit.any ideas? thanks,Troy

P0440, would not cause a stall or rough idle.......

Fact you have a misfire code now, is a whole new ball game......if the misfire is real bad, like under an acceleration under load, that CE light will flash.......

Last COMPLETE tuneup? Check coil output with a spark tester? Check for vac leaks? Check the vac hose to the f/p regulator for fuel? If possible, go to a place like AutoZone if you can recreate the misfire just by putting the car in gear, holding the brake, and increase rpm's to 2000 for about 10 seconds.....with a scan tool attached, it will show which cylinder is misfiring....

P0440 is a Evaporative Emission Control System Malfunction code.
What it basically mean is that you have an air leak in the fuel tank, or a faulty solenoid. Basically, the venting of the fuel tank go to a canister that absorb the vapour. From time to time the ECU trigger a solenoid that suck the fumes out of the fuel tank, causing the trapped vapours to go back in the fuel tank, and back in the engine. To test for leak, a solenoid block the vent. A partial vaccum should appear in the tank. If you get a P0440 it mean that when it does block the vent then the vaccum do not reach the set point. This can be caused by a faulty solenoid, fuel cap that you don't tighten enought when you fill up, defective cap, air leak, or faulty vaccum line and other stuff.

It is possible that you have a vaccum leak (hence the P0440), or fuel pressure regulator that is failed. Also, the IAC could have issues. If you do not have misfire code, I'ld be tempted to say that you have too much fuel, so would investigate the pressure regulator first I'ld also check the IAC. Somewhere I'ld also check the wiring and spark plugs. While checking the spark plugs, it is a good idea to compare each other. If one look different than the others then I'ld investigate on why. It might be nothing, it might indicate a problem there. Ex: if one plug is wet, but the others are fine, then you probably have a problem there: you have unburned fuel (or oil, hopefully fuel) on the spark, could indicate a stuck injector or a no spark. Both could make gas smell on the tailpipe.