Mitsubishi Repair: check engine, throttle position sensor, o2 sensors

Question
my check engine light came on. I did a odb2 reading and it showed p421. Everyone that i talk to says that its a bad O2 sensor. Well I changed both O2 sensors and now my engine idle very rough when i'm at a stop. It lopes like in a wave like motion and the rpm increase and drop. It never did that before. what can be the problem.

Answer
Chino: Listen what your car is doing now, sounds more like the Throttle Position Sensor, my repair manual says this... a broken or loosen TPS can cause intermittent bursts of fuel from the injectors and an unstable idle because the computer thinks the throttle is moving. Also once you put in new sensors you then need to reset the computer. You can so that with a sanner or take the neg cable off the battery, wait 5 minutes and then put it back on. I hope this helps and good luck! Linda