1998 C70 coupe P0422 code

[Racerxc70]

I am the original owner with 300000 plus miles the last 4 digits of the VIN are 0744, I have check the vacuum lines and elbows, run fuel injector cleaner, replace both O2 sensors 5 yrs ago ( no problem just did it) new mass air flow sensor, new plugs and wires
Car runs great, but two moths ago the ecl came on code was P0422, I have noticed a slight very slight idle when the light comes on, I have disco the neg cable to clear the light and code it drives for 40-60 miles sometimes longer sometimes less and comes on again, is it the CAT or maybe the rear O2 sensor, no rattle from the CAT or rotten egg smell

[kahl]

On my 2000 V70 Xc I had a similar problem. New O2 sensors, Cat is good, fixed all intake and exhaust leaks such as exhaust manifold gasket still got p0422. In desperation I installed an O2 spacer on the rear O2 sensor and the car does not trip P0422. Got the spacer from IPD.

[Racerxc70]

I performed a more detailed inspection of the vacuum lines, as owners of the C70 you know that there are numerous vacuum lines for the emission system, some are rubber vacuum tubes and some are hard plastic vacuum tubes connected to rubber vacuum tubes that connect to metal tubes, with foam rubber sleeves for protection in key places. I found a plastic line that had been most likely crimped and broken ( damn mechanics ) it was repaired (bridged) with a rubber vacuum hose tube that was too large (damn mechanics) the plastic tube vacuum line could not seal, I replaced the rubber vacuum hose (bridge) that was too large with one that had a much tighter fit. My guess is that this was broken years ago when my cruise control rubber vacuum hose was replaced with a hard plastic purple line ( a factory authorized fix ), I say this because right after that two codes started appearing, one was a massive evap leak that appeared every few weeks or so (11yrs, I would clear the light by disconnecting the neg battery cable when emissions testing was due, you do what you gotta do) last year I replaced the PURGE VALVE after reading several forum posts, the valve was less than $50.00 new and I replaced it myself, no tools required in ten minutes and the massive evap leak code did not return, but the p0422 came back one week later but would stop showing for several months at a time then appear again ( that loose vacuum hose repair ) It now runs great again
I hope this helps someone

[dosbricks]

Someone I know with an aftermarket performance cat on their 850 wagon would get P0422 every few months. Like kahl, it was solved with a 1-1/4" spacer under the rear O2 sensor.