99 Focus 1.8 runing poorly, pinking, no power

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My partner has a 1999 Focus 1.8 16v, now on 125,000 miles, with full history, mainly by me as a professional motor engineer. (I've always preferred the 1.8 and 2.0 to the smaller engines due to its iron block, keyed crank pulley and separate exhaust manifold by the way, just a shame the idle valve and oil filter are more difficult!)

Anyway I have always felt the car has been down on power ever since she bought it 5 years and 85,000 miles ago. But it was only on a recent holiday I was alarmed by pinking under load. And if anything power seems to be even less now, a guy in a 1996 1.3 OHV Escort could easily keep up on the M5!

I fitted a cambelt kit at 80,000 and last week double checked the timing with the locking pin/bar just to see if a cam was a tooth out on the belt. But it was perfect. I drove the car with the air mass meter disconnected, no noticeable improvement and pinking still there. I have checked for stored fault codes, there are none, and the lambda sensor seems to be switching as I'd expect.

I'm racking my brains, I was considering low fuel pressure but our fuel pressure test kit was stolen in a massive break in some time ago, so how likely is it that the pressure is down? Filter regularly replaced. The car doesn't missfire. So I'm thinking, cam sensor? Fuel pressure? Air mass meter? Lambda sensor? Air leak (though I've looked....)?

Also the car has ongoing idle problems as do lots of these cars it seems to me. It was much improved after fitting a new genuine control valve (don't bother with trying to save money with the aftermarket ones, I've done it to a few cars and it's never worked out). However the engine can hunt a bit at times, revs can remain high in gearchanges too. But worst of all is if the air conditioning is on, sometimes the car will 'idle' at 3,000 rpm, and always idles excessively high while the a/c is on, maybe 1200 rpm. Unfortunately this is now taking its toll on the clutch, another weekend job for me!

Anyway, many thanks in advance for any pointers.

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Bump. Can no one shed any light?