I replaced the O2 (Bosch 15097)sensor in September '09 when my check engine light came on (threw a P0133 code). Car had about 146,300 on it at the time. Check light came back on after about a week. 2K miles later, I had the car checked at a garage and they found no issues other than the O2 sensor. After 2K+ miles, the car still runs strong , but my gas mileage has plummeted. Is the sensor the culprit? How long can I wait before doing damage to the cat converter?

Before you throw more money at it, check all of the air lines around the intake manifold for cracks and light leaks. Including the air hose from the cleaner to the throttle body and the vacuum tree. Any leaks will compromise the system and your car will run rich.

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.

Hello,

I've been going through this as well... do you have an air pump? If so make sure it turns on when starting from cold... if not test it make sure it isn't full of water... check the purge valve on the radiator shroud it has two vac lines to it one with a check valve- this part was bad on my 855 na and it cause hesitation and fuel trim issues.

good luck and please post your findings!

greendread