I'm trying to diagnose a problem with my 98 V70XC.
I did some work to replace the PCV system as the vacuum lines had cracked through. This included removing the inlet manifold and replacing with a new gasket. Shortly afterward the car was running a bit rough and then threw a check engine light. The trouble code was for the front O2 sensor circuit.
I cleared the code and thinking I may have introduced the problem, I removed the parts again that I had fiddled with to get to the PCV. On the way I checked as many vacuum connections as I could and reinstalled the inlet manifold with a new gasket again. I'm pretty sure I got the inlet manifold back on correctly and gave the bolts a little extra torque than spec just to be sure.
After all that, the car seems to run a bit smoother but the O2 sensor real time readings are still looking problematic.
At idle the front O2 sensor is varying wildly from 0.3V to 0.6+V and the stft is also varying.
The rear O2 sensor is rock steady at 0.485V.
Any opinions as to whether this is more likely to be a vacuum leak that I haven't found or a faulty O2 sensor?
Would a bad O2 sensor cause the rough running?
TYIA and pardon my ignorance.
[Edit] With further reading, perhaps the front O2 sensor's behaviour is normal? Anyone know how it should behave? At idle should it be a slowly fluctuating value or rapidly changing?