170bhp pd passat rough idle and clicking sound

[dfgrout]

hi guys

i just bought a Passat B6 wagon 170bhp tdi SEL today.
it all seemed fine on the test drive and the drive home. got full VW history and at 97500 on the clock.
sat in it on the drive once home and the idle seemed rough if not nearly spluttery as though it wanted to go all lumpy. this is to the extent where it makes the car throb. this goes when revved and also is consistent whether the clutch is pressed or not.
there is also some intermittent random clicking or ticking noises coming from somewhere at the back of the engine or behind the dash (only audible from inside).
becoming paranoid i looked at the exhaust and the some vapour/smoke seen but not anything major, it all smells a bit though.
also filled up full about 15 miles before i got home and its now saying 3/4 full.
any ideas? i need help!!