Yes im 100% sure it is because of the pcv fix. The day i fitted the fix it started spluttering slightly and gradually got worse, so then i refitted the standard pcv and it was ok for a while, then a day or two latter every time i used over half throttle it would misfire really badly and backfire.
So i bought a new pcv which improved it a lot, which is pretty much how the car runs now.
I have only heard of one other case where this has happened, it must have been due to the rings been weak to start with then the pcv fix finished them off.
Has anyone got any ideas of the cost to sort this?