[giz]

thanks for the reply.

This reason i started all the work was because of this fault.
The car starts perfectly, doesn't smoke or rattle or bang.
It does have the odd whiff of burnt oil but i think that is the front cam cover gasket spitting oil on to the manifold.
engine oil was changed a few months ago when i bought it, the level is currently about half way between min and max.
I've reset the ecu today and taken it out for a test again. Temperature doesn't seem to affect it, it did this from cold.
At really low revs when this fault occurs the car runs fine ,all be it like an old woman on the way to a church jumble sale.
revving just makes noise and no power, too much revving causes it to splutter, yesterday the fuel pipe popped off but that might just have been incorrectly fitted.
so, after driving like an old lady for 10 miles the fault went away and the pedal feels lighter, the car bursts into life and i drove like i'd stolen it. Then, i slowed down and changed into 2nd at a small island, pulled away gently and the fault is back for the rest of the journey, 2 miles or so.

also, rev range.... anything above 2k gentle acceleration produces this noise, drive it with barely any throttle and it will happily rev past 3.
3.5k with gentle acceleration causes a splutter.
i don't think it's a timing issue as the fault comes and goes.

oh and the original flap broken cleanly, i guess these were designed to fail to safety, the shaft snapped in a cone shape and stayed inside the motor.