320i rough start up

I have just purchased from a mate an F reg Bmw 320i tourer. The car has come with 12mths MOT but has not been used much in the last 3-4months. When I started it this morning the engine started ok but was mis-firing
whilst driving and it even back-fired a few times. After a short run it eventually cleared and was great after that. Is the problem likley to be just leads or something being damp or worn? HELP!
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I little bit of oil trickling down a valve stem seal or similar.
Of course if you rev' it when cold...
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