I have a 2000 Pontiac montanna van it runs great on long trips where your not having to stop but as soon as u come to a stop it starts pulsating up and down till the motor stalls? It use to only do that after a long five hour drive now it does it every morning while its warming up! After about 10-15 minutes of being warmed up it starts pulsating the tack goes up and down till it stalls out! It will stay running if you keep the idle up with the gas pedal! I would like to know what parts I need to fix this? Some people say its a air sensor or fuel pumps weak ignitions going throttle body needs cleaning? What do you think?