I fitted the correct lambda probe for MEMS2J as the one I had was for MEMS3 and wasn't giving a reading.
Good news is that it is giving a reading, bad news is that the car is still running rich at fast (2500rpm) tickover as it is still running open loop at that speed rather than switching to closed loop.
Something so simple yet it is keeping the car off the road.
Throttle sensor? not sure what else you can change as you been down all the usual routes James. Is your F a Mk1 with a distributor?
Sundance
Have you low fuel preasure?