On Friday and Saturday I managed to check that the exhaust definitely had no leaks and have a look at the other issues you guys raised.
As the customer lives in Bristol (a 2 hour drive from me) I wanted to make sure the car would be fine for him for a while so I replaced the thermostat and temperature sensor for good measure.
Whilst working at the front of the engine I whipped-out the whole breather assembly and cleaned all the pipework and examined all the valves.
It turns out, as a few of you had already anticipated, that the crankcase breather valve (PCV?) was only intermittently providing a one-way seal and that the pump that this fed (the 'suction jet pump'?) was absolutely blocked solid on the input from the PCV. I replaced both and the car seems now to be sweet as a nut.
My only regret is that the customer picked up his car on Saturday lunchtime and I didn't get a chance to see if the engine load, injection time & emissions readings had improved etc. Darn! Hence I am this stage reluctant to say that the car is 'fixed' only that it definitely was idling much more sweetly.
By the way does anyone know whether or how a pressure transducer connected to Picoscope might have helped pick-up the fault non-invasively? - I suspect there might be a way!?
Thanks again to everyone for their help.
P.S. Mark, my customer did get his AC issue sorted after speaking to you contacts in Wales - thanks.
