O2 sensor error codes and corrections

Hello, I just bought a '92 taurus wagon. I got it for a good price because the check engine light came on frequently and it ran rough when the light came on.

I checked the codes and got 172 and 176 which appears to indicate that both O2 sensors are always showing lean. Now I have purchased the sensors but have not yet installed them. My questions are, is it likely that both sensors have failed? What would the symptoms be (apart from the indicator light)? Could something else be giving me this reading? I don't want to waste the $100 it took to buy the sensors if it is not likely to help.

On another note, the car was recently smogged and failed the HC portion by about 15-20%. The NO and CO were fine. I would imagine bad O2 sensors would cause the car to use too much fuel and screw up the emissions.

I appreciate any input.

Thanks,

DJ

I'd say if the EGR valve was closing properly, then an O2 sensor could be giving the codes.

Just a quick update. I still haven't installed the O2 sensors as I don't have the place just yet and I'm still not completely convinced that they are the problem but I did clean the idle solenoid on top of the intake manifold. It has made a significant difference in the driveability of the car but it still idles rough and has little power. The engine light still comes on too, I'm guessing that it's still the 02 codes but I haven't checked for more. I also checked for vacuum leaks and found none. If anyone has any further insight, let me know.

DJ

If your car has a Mass Airflow (MAF) Sensor, you may want to CAREFULLY clean that. I'd also suggest you run a bottle of fuel injector cleaner through the car and see if that helps. You may have some restricted fuel injectors.

A tune up would likely be money well spent too. You should at least inspect the spark plugs, spark plug wires, and fuel filter. If any of them don't look nearly brand new, replace them.

Just because your O2 sensors are reporting a lean mixture in the exhaust does not mean they are the problem. Very likely something upstream from them is causing the problem, they are just reporting it. If the codes are in fact reporting lean (I have not verified the codes) you probably have a fuel restriction, but don't rule out plugs and wires.

What method did you use to check for vacuum leaks?

Do you have a vacuum pump? If so, per corning_D3's suggestion, you may want to pull a vacuum on the EGR valve at idle and see if the engine runs worse (or dies).

-Rod

Ok, update number 2. I just finished changing the spark plugs and cleaning the MAP sensor. I'm not sure which one did the trick but it's running great now. I haven't cleared the codes yet but I just did a test drive and it runs like a champ (well a 14 year old champ with 126000 miles). I suspect it was the MAP sensor since the plugs looked really good. Either way, I will take the O2 sensors back and get a refund if I don't throw any new codes.

Yeah!!


DJ

Next update. I just got back from getting the car smogged. It passed, no problem. I'll probablyl take the O2 sensors back since I need some other parts for the car. It still runs good and strong. :p

DJ