|Originally posted by Formula88:|
Nope. The ECM has no way to know if you have a catalytic converter or not. The O2 sensor is before the cat.
Check the code to see what it is. What's your idle speed? Could be an out of adjustment IAC or TPS. (Idle Air Control or Throttle Position Sensor)
Idles about 900 and smooth as silk. Guess it's all the more reason to swap in the 4.9 ( )