I've noticed a loss in power lately but a few days ago I was dropping someone off and when we arrived we sat in the car for a good 15 minutes or so with the engine running. The outside temperature was cool.

When I drove off, the increase in power was quite incredible - car felt very light - lots more torque - but it only lasted a couple of minutes and now it's back to normal.

Any ideas why this might be? And how can I get the lost power back?

Thanks in advance for help/suggestions.