iv come across this a couple of times can anyone explain iv got a uk turbo 2000plate how can u tell if your car is affected

 

You get piston slap when the piston to bore clearance is to great, what you are hearing is the side of the piston hitting the cylinder bore. This can be for various reasons, wear for example, you can also get piston slap when running high performance forged pistons which is quite normal due to theyre design. The reason in most cases the piston slap goes away is because the piston expands in the bore due to heat and reduces the bore clearance.