Question about o2 sensor cel codes

BWB95GT · Apr 30, 2011

I have been having idle issues and just generally running rough with a car I just bought. The previous owner told me that the MAF sensor was bad, so I replaced that immediately and no change. So I cleaned the IAC, and still no changes. I checked for vacuum leaks and didn't find any (though it was the first time I had ever checked, so there's a chance I missed one, but I don't think I did)

So I checked the CEL codes and I ended up with 172 & 176 right and left heated o2 sensors reading lean. My question is, should I just replace the o2 sensors? Or do I need to figure out why my car is running lean? I really don't want to blow any more money on something that wont fix my problem.

Any help would be greatly appreciated.

BWB95GT · Apr 30, 2011

It's also worth mentioning that it was the first time I have ever checked codes, so there's a chance that it was actually codes 72 and 76 if the CEL flashes once prior to giving the code (I wasn't sure if the first flash was part of the code or not). Those would be insufficient manifold absolute pressure (but wouldn't replacing the MAF have fixed that?) and insufficient vane air flow.

Which of the four codes mentioned sounds most like my problem?

toyman · Apr 30, 2011

The codes should be 3 digits. The O2 sensors may be correct in the lean reading. That would put the problem elsewhere. Since you don't know if the codes are current or not I would remove the negative battery cable and let the car sit for 15 minutes. Hook up the battery and drive it for 1/2 hour and then pull codes. That way you will know that any code is pointing towards a current issue. Until you do this but you can only guess at solutions.

Addermk2 · Apr 30, 2011

replace the O2 sensors

rz5.0 · Apr 30, 2011

if you are running lean you could have a vacuum leak. but it never hurts to replace o2 sensors they are the most neglected thing on a car.

BWB95GT · Apr 30, 2011

I did clear the codes before I checked, so I know those are current. So I should swap the sensors either way?

BWB95GT · Apr 30, 2011

I just need upstream sensors to fix my idle problem, right? Or should I replace all four?

rz5.0 · Apr 30, 2011

94-95 only has two before cats. not 100% that it will fix it but never hurts to replace and narrows down the prob if it does not.

toyman · May 1, 2011

Just remember there are hidden vacuum lines in both fenders and behind the heater A/C control panel so it's easy to miss a broken or cracked line. As well the EGR control is also hidden and can be a cause of a bad idle if it's not working properly.