Nothing to do with more expensive petrol? The wife was filling up and that BP ultra stuff untill she noticed it was 10p a litre more the regular unleaded.
I've been advised in the past that if you fit a new potentiometer you should disconnect the battery to reset the ecu then when you reconnect it, switch on the ignition and fully depress the accelerator pedal a couple of times to register it's setting with the ecu.