Intermittent surging under load 2007 XC70

[jonesg]

I would replace the turbo coupler , $60 approx. Inspect turbo hoses and plumbing, get your hands on them, visual inspection won't reveal leaks.

[abscate]

The LPT on the XC70 boosts low to help get the big beast moving. It does sound like a tcv replacement is in order. It isn’t an aftermarket is it?

[JHarkness]

Just thought I'd give an update. A new TCV resolved the surging issue, though I'm now chasing an underboost issue (I'm assuming there's still a leak somewhere in the vicinity of the intercooler, or it's sensor related). First time with new TCV, car boosted smoothly right up to 10psi. Since then I've been able to get it back to 7-8psi after an ECU reset but it will no longer boost above 5psi after driving for about half an hour, sometimes not above 2-3psi.

My fingers are crossed that replacing the PCV system resolved the oil consumption issue. The drain from the oil trap into the oil pan was completely blocked, so any oil in the system was just getting burned, check valve in the banjo bolt was seized, but neither the intake manifold nor turbo circuits were blocked. Didn't find any vacuum leaks either. I've driven it over 1,000 miles since and the oil level has stayed essentially the same and is cleaner than it was after the same distance before the PCV replacement. Also switched to 5W-40 and used a RMS stop-leak additive -- can't see any fresh drops of oil from the RMS now.

Also had a FPS go bad right after replacing the TCV. Would spike to 111psi and the car would almost stall, it seems that it was experiencing some hesitation related to the FPS at full throttle while the surging was occurring.