I have an 89 Rs with a brand new gm V6 put in 7000 miles ago, sometime the service engine light is on and when it is car idles rough and sometimes stalls when I come to a stop, But sometimes I start my car and the lights no on and the car runs and idles normal, I've changed the MAF, Throttle Position Sensor, O2 sensor all with no luck any help would be very appreciated