OBD says running rich

Running rich means there's too much fuel going through or the right amount of fuel going, but not any or enough kind of air going in, so you got an air restriction somewhere, air filter replacement is right, but there's more than that, like the air intake needs to be cleaned out, or a fuel problem were too much fuel is going through. Your gaskets could be a problem too, but I can't pinpoint which ones. Check the exhaust system, there's bound to be a problem there.

Have a look at what your O2 sensor is reading. It should be bouncing roughly between.2 -.8 volts. It makes voltage in the absence of oxygen so try and force it lean by removing a vacuum lne from teh intake and wach the voltage it should drop way down.