I will try this. Just for confirmation, the MAF is the thing plugged into the air filter housing?

Cat being catalytic converter?

The engine buildup they said could be due to using low octane fuel, but I always fill my car up with premium (costs a bloody fortune). So unless the fuel company is fuel swapping and ripping me off, it must just be bad luck.

Thanks

+Edit+
Just discovered that they did investigate the MAF and clean it as part of the service done yesterday.