1998 S70 CBV related MAF issue

[gadza]

Hi everyone,

I've had my S70 T5 for 7 years and always fixed everything by myself.
Except for this one which I don't know how to deal with.
A short history:
After about 100000 km of driving without any problems, the car lost it's power.
It turned out that there was a huge hole in the rubber hose which is connected to throttle body.
I replaced all the hoses (they were very soft and oily inside) and everything went back to normal.
Later I suspected that beside the fact that the hoses were old and weak, a faulty CBV might be responsible for the hole.
So I examined the diaphragm in the CBV which had a hole as well so the vacuum from the intake could not open it,which caused very high pressure in the intake with closed throttle after boost.
I replaced the diaphragm and the spring.
I just drove 100km and the car stopped.MAF problem.Disconnected the MAF and drove home.
Ok,it was old,I bought a new one,OEM Bosch as well as an OEM oxygen sensor.
After 200 km,MAF fail again (the new one). I cleaned it, car worked well for the next 200km.
Then the engine suddenly seized due to crankshaft bearing failure in the 3rd cylinder when it was without load and around 1500rpm.(Yes it made a knocking sound for a few seconds on each start which I thought came from the lifters but otherwise it was unexpected.The oil was fresh,I think it happened due to very high mileage.It was the Italian version B5204T3,225HP and with these engines I heard this is a common failure point.Never mind.)
I replaced the engine with a B5234T from a 850.I mention it because the issue with the MAF persisted.
So I suppose oil fog is blown back to the MAF now that the CBV is working and covers it with a thin oil film,which eventually leads to failure.Where does the oil come from? There is oil in the hoses after the turbo for sure.
First I thought the turbo was leaking oil.So I replaced the CHRA with a new one.(Not chinese of course).
It did not solve the problem.I also replaced the valve stem o-rings (and the lifters hence I worked there).
Then I replaced the whole PCV.It was not clogged,though.There is some smoke from the dipstick if I unplug it at idle, but is intermittent,most of the time nothing comes out. I also replaced the rubber seals for the oil pump hose,the sump seal,the camshaft seal,the whole ignition system,timing etc as Stage 0 preparation.
The newly installed engine is nice light brown-yellow-pink inside.It does not have visible exhaust smoke.
It is silent.The injectors are responsible for most of the audible noise.
I flashed the ECU with 2.3 firmware with slightly altered boost map (motronic suite), the car runs well, top speed is 247km/h by the tacho and most of the times it loses the grip in 1st gear at full throttle (it's 4 spd automatic), so I guess engine is in good condition.
But I need to clean the MAF in every 200km if I use it in city, 500-1000km otherwise, and reset the MIL.

There are workarounds,which I don't want
- to remove the vacuum hose which goes from the intake to the CBV.It would blow the hp hoses and kill the turbo after a while.
- to install a blow-off valve instead of the CBV because the ECU would flood the cylinders with fuel which washes away the oil from the cylinder wall.

This is more than annoying.Please,someone,help!
Do I need to rebuild the engine (overbore + new pistons and rings) to fix this problem?
Thanks,
Arnold

[chrafael]

On my V70 I disconnected the two pcv hoses at the intake hose, capped the nipples, put a length of hose on the large pcv hose and routed it under the car like a draft tube. You shouldn't see much if any oil coming out of it. If this dries out your maf, suspect blowby. Also cap the small vacuum line or as I did hook up a vacuum gauge to it routed to inside the car. My lpt reads vacuum most of the time with a smooth swing to boost under acceleration, and instantly back to vacuum when I snap the throttle shut. Anything else would make me wonder about the tcv or its hoses. Just a thought.