Cleard a fault code!!!!!

You probably all aready know this but....

Been experiencing some sluggish behavoir from the Clio recently So I set out to diagnose the issue everything from ignition to exhaust. After replacing the obvious (sparks, coils etc) I got a little fed up and decided that I might get rid. I borrowed a VI Monitor off a mate and had a play. Found a fault code. P0300!!!!!! Tried to clear it off but kept popping back on. I turned the car off and tried again. Presto, the code had dissapeared from the screen. Drove to work in the morning, wow, the car was responsive, and punchy. Loving it again. I suspect that this has been on and off since I changed the de cat to sports cat on the Milltek system, just didn't realise.

If you suspect that the car is slower than normal, then try checking the ECU for faults. Has anyone else experienced anything like this? Is this a common fault and I'm being a bit slow off the mark. (No pun intended)