Chevrolet Repair: Cavalier Too Rich, chevrolet cavalier, tailpipe emissions

Question
1998 Chevrolet Cavalier 2.4 dohc. Check engine light on but running fine. OBD Code po172 set (rich condition). New plugs and air filter. IAC, EGR, and throttle body cleaned. What should I try next?

Answer
Hey,
 
 could be a defective 02 sensor.  They don't last forever and manufactures spec used to be 80,000k.  The sensor should be checked to see if it matches tailpipe emissions.  It will fluctuate from .3 - .7 v at idle.  If the sensor is stuck rich it could be defective or actually is running too rich.  Check fuel pressure regualtor for fuel leaking and too high fuel pressure.
w