ok so after i added MMO to the tank and that caused my O2 sensor to be fouled and run the GTA rich for a while, i replaced the O2 sensor that helped but has not solved the problem completely my the GTA still idles rather high it is mostly on 1000 rps rarely droping to 800 rpms when is completly motionless and since i run the car with MMO its harder to start, in the first crank as soon as i turn the key i hear what seems like a misfire and then in a second try the car starts right up what could cause these things its a 5.0 5 speed

 

This probably doesn't have any thing to do with it but how do your plugs look?

 

oh yeah i changed the plugs after having this problem