i have a PLX M300, and i had it mounted right by the factory O2 and it was reading perfect, then i switched it to my other car and the exhaust only comes to about the shifter area.................well i mounted it right at the end, which is under the shifter, and it wouldnt read worth a ****??????

THE EXHAUST IS A CHERRY BOMB, AND IS ABOUT 3 INCHES, COULD THE EXHAUST BE DISSIPATING BEFORE IT HITS THE O2 SENSOR?????

but when i moved it into the header spot it read normal again????

 

ttt

 

Try and rev the car to 5k rpms or so. Get it flowing enough and see if it reads correctly. My guess on it is that the air is circulating around it at idle since the exhaust flow is minimal and you are not getting the correct readings. Sending you a pm too.

Jason