1998 cavalier 2.2 stalls @ stop

[STEVE099]

I have a 98 cav rs 2.2L. When I come to a stop or am just starting off the engine will begin to putter and struggle to stay on. When this happens the brake pedal goes limp and presses down to the floor with no resistance. Last time this happend I rolled out in to traffic. Happens more frequently/intensley with AC on. Also, this puttering/struggling of the engine also happens when coming from a stop if I gently apply the gas pedal. When I push further down on the pedal however the car will run fine. I have no trouble at long distances or highway speeds. The car is giving out no codes which has made the diagnosis very difficult. I could really use some help.