Renault clio

[rich1985]

i can smell petrol fumes in my car coming from the air vents, but it only seems to be when im going slow , can you tell me why this is please

[Tim Baxter]

Are you sure it's petrol, it could be ehaust fumes?  Either way it's lethal situation.  If it's exhaust it could make you drowsy, at worst unconcious.  Without being clever, if it's petrol it's being sucked into your car from outside.  This very dangerous because petrol knocking about under your bonnet is a very real risk of causing a fire, it may even explode.  Your hot exhaust or a spark can cause this.  Do not run your engine until you have sorted out the problem.  Good luck.