Fuel Filter (3)

After changing the fuel filter and after the 200 mile trip to pick up the hardtop, I noticed that, when hot, the idle speed rose to 1200rpm falling to 850rpm after a few seconds when slowing down to stop. Not good. After taking advice from the forum, have now sprayed a tin of carb cleaner into the air intake (cleans Idle Control Valve?) and reset the 'base idle'. Result - perfect! Now, was it the change of fuel filter or the long run that caused the problem? Having been on a previous run up to York, I have to probably say it was the change in filter but the reasoning is a mystery - any comments from the experts out on the 'net?