clk270 cdi

Hi all, I've had a look around but I can't find another problem quite like this. Every time I start her up the revs drop just below where they should sit for about 3-5 seconds which makes the car really rattle. It's fine after that. Any ideas? It's a 2004 with 121k on the clock. It had the...

Wonder if anyone can offer a glimmer of hope as I'm feeling like a bit of a mug... Having been made redundant for Christmas and had to hand in the company car, I bought a 2004 CLK 270CDI on autotrader from what was supposed to be a private seller. The car was in London and I went up by train...