After a couple of weeks of ownership of my 2006 V70R, I dropped it into the local Volvo specialist for a check over. They discovered an issue holding a fast idle. When revved to about 2500 and held, it drops the revs to 2100 quickly, then returns. This fluctuation continues every second or two. They diagnosed a possible issue with the Cat.
There are no relevant codes in VIDA, just a couple related to the A/C not working, which I know about. There only other symptom I have is it smells a bit 'fuelly', but I don't know what a 16 year old V70 should smell like.
I've tried to test it using VIDA, but don't know enough about fuel trims and O2 sensors to diagnose reliably.
The initial sharp fluctuations in the rear sensor (blue line) show what's happening with the symptoms in the video. The second half of the trace is under normal idle. I think this is normal behaviour, but not 100%. Can anyone help explain what's going on here? Should the reading from the front O2 sensor be so flat?
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