ive never had that problem. i too have an AT/w ss, and i had a viper alarm installed with autostart and ignition/fuel-injection cutoff. if yours did too, maybe they messed up the wiring since alot is done under the hood. but either way, COMPLAIN. they obviously messed up your car somehow if it wasnt doing it before. professionally installed means something depending on where you get it done, but even the best might mess up every now and then.