Suffered quite badly from this today. Did an hours drive, stopped for an hour and then had really lumpy idle. Drove for 20 mins, stopped for 20 and same again. Then drove for an hour again and stopped for 10 mins and it was fine. Whilst I do quite like the car's shake and the lumpy low idle noise it makes and the burbling when you bring the revs up with no load it's probably not generally good for the car. It does seem quite random as to when it does it, and it's more frequent since I had the kenne bell heater bolted to the top of the engine. I have no insulation under the bonnet, and plan to fit some vents if I ever get round to having some body work mods done, so will be interesting to see if this helps.