Not running it up through the rev range could be the cause. As far as I know, turbocharged engines need to be taken right through the rev range as the turbo will only receive clean oil when in use. Another knock on effect is the build up of carbon deposits in the cylinder head and exhaust. The pressure of the gas at a few thousand RPM maintained for a period of time (a.k.a. a trip on an A or M road) is needed to force the deposits out the system. An unused engine will clog up and struggle to run if left. Maybe run some Redex through the system to clean the deposits out.
I could be very wrong, but its what I've always been led to believe. So in short, yes, go for a drive every now and then.
