Mine had been losing power on hills for some weeks, but since I do as well, and its nearly as old as me I put it down to old age! Today it suddenly wouldn't go above 3000 revs (guessing that figure). After reading through these blogs I opened the air filter case only to find the filter itself breaking up badly. Took that out, but still no revs. Took pipe work to turbo off, found bits of 'fluff', and then to the turbo where I found chunks of air filter, so much I could have used a spade and dug it out! Once cleared runs boootiful! Mind you without an air filter in there it sounds a bit boy-racerish. Going out to get one now.
Dr Quartz, August 2016