Right then, an update. I think I've licked it. Had a good day yesterday..!
A friend of mine runs a garage, so I occasionally can go down on a Saturday and use the facilities if there is nothing going on and one of the lifts is free.
My job list was
New Plugs
New Coil
New TDC
Check and clean all electrical connections.
Get engine bay cooling fans sorted (Sensor and blower were both NFG)
Did it all.
The car had incorrect plugs fitted. They were single electrode and according to the NGK parts book not for this application. There is a special note that A610 application should be triple electrode and the new plugs going in were correct spec. (£20). The ones that came out were all the same in appearance and showed the engine is in good order. So some good news there.
The coil clearly had been on the car a long time, and as they are so cheap (£20) I figured id just swap it out anyway.
I gave all the engine harness and every connection a very thorough inspection and didn't find any real horrors. Some areas of the loom I have rewrapped, and I gave each connector a good clean too.
I pulled my TDC sensor off the car and replaced it with one I eventually found in stock at the EuroCarparts that's less than a mile from my house. (£6 ! ) It was a genuine Siemens part but did not have the heatsheilding, no drama I thought I can just swap out the heatsheilding off my car onto the new sensor. Once I got my sensor off the car, there was no heatsheilding on it all. Fortunately I have plenty 'stuff' in my garage collected over the years working in motorsport. I have managed to make a very nice job indeed of heatshielding the sensor installation and its wiring using really high performance materials more often used for insulating wiring and other components near the exhausts on F1 cars. Really hapy with what I achieved with that, I certainly have the best insulated TDC on any A610 I should think.
I also swapped out the engine bay cooling fan for a good replacement. Mine had about 5mm side movement in the motor shaft, no wonder it was so noisy! With a new 90degree temp switch (£7 ebay) the cooling fans are now working correctly. They come on and go off periodically in traffic, and start about 2 mins after stopping and run for about 10 mins.
So, for about £50 spent, and a hard days work, I think I now have a car that's working properly! I've done about 100 miles over four journeys since I finished the work yesterday PM. Ive also deliberately got my self into situations where I know that previously the car would have been damn near undriveable. And its been good.
I currently don't have the earth strap on the fuel pump relay. I don't appear to need it.
I think its certainly clear then that the 'A610 cutting out' issue has numerous potential root causes. Which explains how its such a difficult thing to nail down.
Hopefully, for now at least, my car is going to be reliable.
Steve Barker will probably be gutted, I reckon this was a very significant part of him selling this car.
I also fitted some new rear tyres and removed and refitted the fronts too rebalancing the wheels and sorting out the slow leak from one of the valve stems. I put Bridgestone S-02's on there, as Jeremy Clarkson once said.. "To anybody who says a tyre tread pattern cannot be sexy.. You've clearly never seen a Bridgestone S-02."