Evap emission control system malfunction

[95 GA/TA]

I thought i would run this by you guys and see what you thought.I have the 95T/A and a 1998 chevrolet ext cab 4x4, 350.The ses light had been coming on and off for a while and id never got a chance to check it.Well recently the truck started hesitating and stumbling,seems to do it more when cold and clear up after it gets hot.And it doesnt do it all the time,i checked the truck and came up with the code= evap emission control system malfunction malfunction,po 440,mod $10.I have looked around and this seems mostly related to a leaky or not tightened fuel cap.I know this isnt an f- body but i know there are some smart folks here and if you would share your opinion i would appreciate it,you guys have never let me down before.I just am wondering if the light has anything to do with the running problem?If anyone has any ideas please let me know.I really dont want to take it to a dealer.

[Kevin - Blown 95 TA]

I'll make an educated guess based on your information.
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If you gas cap is in fact leaking fumes out: When the PCM commands the solenoid to purge the cannister of fumes periodically into the intake manifold, the fumes are replaced by a less rich mixture or less pressure - The PCM is expecting a rich mixture and backs off the injectors, but instead it is getting less fumes from the purge solenoid and really has a lean stumble. This would be worse with a cold car.

[Maverick_82]

Is your EGR unhooked?
My trans am experiences the same hesitation and i think the unhook EGR valve is to blame.