Thanks gents- to answer:
No this is with the standard air filter . A friend (of Craig's) connected a professional OBD reader and no faults showed up. He cleaned the airflow sensor. Then I put in some petrol additive and filled the tank with 3/4 of a tank of 97 octane. Then I blasted up and down the A34 at 5500 rpm to perhaps clean out any clag in the Catalyst. (Including hitting a huge pothole which bounced the car so hard that it triggered the fuel shu off valve - very dangerous and it's been there for a long time, apparently). The problem is still there.
So Heinz, I think I should check the connectors on the throttle valve - but, where is this, please?
