Porsche Boxster Running Rough, Starting & Power Loss Problems

Engine has knock on start up when cold ,if restarted within two days all is ok leave three days knock is back sounds like a big end but only knocks on start up all ok when running and high or low revs I have had new timing chains fitted as...

when i start the car from cold the engine rattles for half a second then runs smooth.Is there something wrong with the car

In heavy traffic the car lost all power, there's no warning, no strange noise nothing. It happened several times in heavy London traffic before I had the car flatbedded to the Porsche Centre. They had the car for 3 days, ran a load of tests...