I have a 2003 Honda Accord EX 4DR 4 cylinder with over 170,000 miles on it. A week ago the check engine light came on. The car still ran like normal. I checked the code over the weekend with my scanner and the code was P0420 - catalyst below efficiency. Well I figured that I could just reset the code and see if it came on again. I have been driving it for a week and the CEL has not came one again. However, ever since I reset the code once the car gets up to normal operating temperature when ever I stop at a stop light/sign it feels like it is about to stall out. The idle is lower than normal around 400-500rpms. Also, when I put it in park or neutral the RPMs drop down to 400-500RPMs then after about 15-20 seconds it will correct itself and idle up to around 700-800RPMs which is normal from what I remember. I am not sure what it is. I was first thinking it was my O2 sensor in the catalytic converter? Could I just unplug it to see if it acts better then replace it if so? I know the code usually means to replace the catalytic converter but I didn't have any symptoms until I reset the code. I was also wondering if it could be the IAC valve?