A MAP sensor is an manifold absolute pressure sensor that can cause a change in the vehicles performance. It can do anything from cause poor performance, shut the engine off to exactly what you described. Its purpose is to provide the right amount of fuel and adjust the ignition timing based on intake vacuum. If it advances the ignition timing a slight amount at the wrong time, the engine RPM could change.
Please keep in mind, I'm not there with you, so I'm doing the best I can. If your local mechanic feels differently, let me know what he says and I'll try to guide you from there.
I hope I helped, and look forward to hearing from you in the future.
Wednesday, October 1st, 2008 AT 5:09 PM