Im being told that my 4 year old, 31,000 mile Astra 1.8 16v needs the 'Throttle Body' cleaning as it has become clogged. I asked if this was a design fault that it should become clogged but was told it was because I only do short journeys, to which I countered with nobody told me the car would develop faults if I didn't do long journeys... I seem to have no choice but to pay the bill but should this be an acceptable problem?