Yes - Bosch filter installed which went on fine.
This will not be a valve/rocker issue,nor will it be low compression and removing the rocker cover is quite involved and needs £££ of gaskets to replace,i would be looking at air flow restrictions on the inlet and exhaust sides of the engine before spending money on it,egr valve can stick open,dpf/ cat could be in trouble,inlet pipework can block up and the inter cooler is prone to splitting causing running problems,I really hope you can fix this car without too much aggro,I take an interest cos I am a v70 owner scince last year and it has been the most troublesome car I've ever owned by a mile.
I think you could be right, but so far I've ruled out pretty much everything on the inlet side apart from the manifold itself by disconnecting the pipework and letting the engine breathe atmospheric air straight into the manifold, if that makes sense? Intercooler looks fine, I took the panel off underneath it and couldn't see any splits/bulges/oil. It's probably worth making more of an effort to get the downpipe off the turbo before taking the rocker cover off, that and taking the air pipework off the turbo to rule out a restriction there. Sorry to hear that about your V70, it's annoying because I reckon it'd be quite nice if it worked!
Does the turbo spin if moved by hand?
Is the MAF code still immediately there after clearing? If not, does it reappear quickly once the engine is started?
If turbo spins by hand and does does freely, I reckon as solid61 said it's likely an airflow issue on either intake or exhaust side.
Haven't checked the turbo yet, I'll have a look next time I'm up there.
The MAF code doesn't come back until the engine has been running for a while, can't remember exactly how long but certainly not straight away. Would I be right in thinking that the reading from the MAF is likely correct but the ECU doesn't like what it's seeing?
I think you and solid61 are on the money, will have to do more checks on airflow next time I'm at the unit.