just curious what could make my car do this. when i stop driving my car will idle down to 1k rpm where it should sometimes. and sometimes when i am rolling to a stop in neutral the rpms will go down to 0 and bounce back up to 1k and then back down again. and sometimes it will get under 500 and it kinda sounds like its going to stall. if its doing this and i turn on the a/c or heat the rpms go to normal. i have my fuel pressure regulator set @ 48 psi. what the hell is causing this.