I start the car up and its fine but after a couple ofinutes my rpms drop below 300 in neutral, I get a funny smell sometimes too.
Code 21 and 51 are both O2 sensor related if I believe, but the thing is I have already changed my only upstream one.the catalytic converter was changed about 4 months ago. I'm cleaning the throttle body saturday. I have a feeling it might be the exhaust as it has a rattles some. Any ideas as what it could it be?