I have just bought a 2003 lsv with a injected 5.7, its the gravity grames edition,But yesterday i noticed i was idling into a bay after about 5 min of idling it quit, when crank it back up, it would idle up and then back down,when i would pull a boarder up sometimes it would sound like the motor was couphing you would have to back out of throttle and get back into it,someone saud it could be a throttle air valve or bypass or something to do with air fuel mixture, all filters are just replaced, please help this sucks