I've searched and found the first one is for the MAF sensor which I will diagnose since Injuneer posted many times on how to do. However P0303 comes up with nothing in the search...any ideas?

The scantool says Cylinder 3 misfire...why would that cylinder misfire. I've just recently changed to a new Opti and thats when these codes started.

Thanks,
Sherwin

 

Cylinder three could have a bad plug or wire. Check that the plug wire is securely snapped on the opti and plug.

 

Cylinder 3 could also have a faulty injector, loose valve, etc. The code is not limited to misfires due to ignition. It detects misfires for any reason, by matching the output signal of the crank position sensor to the known irregularities in the crank's rotational velocity, as a function of the firing of the cylinders.

Also, check the end of the wires for corrosion.