p0421 is the only code my car has thrown so far. I still get it occasionally. It does not impact driveabilty at all. My 2nd 02 needs to be replaced but I have not cats so I'm waiting until cannot pick up any signal. The CEL always goes off after a drive cycle or two.
What kind of intake manifold do you have stock or 626?
Send a PM to hornsfan. He's a cool guy and Mazda tech. Maybe he can give you some other ideas for things to check.
What kind of intake manifold do you have stock or 626?
Send a PM to hornsfan. He's a cool guy and Mazda tech. Maybe he can give you some other ideas for things to check.