2.25 diesel misifre? timing? injs?

Evening all,
I had a search through the forums but couldnt find anything relating to something ive noticed. I did a big trip about 400 miles yesterday all round in my 2.25 diesel SWB S3, on startup its got a misfire and smoke but it totaly clears when it warms up with no apparent misfire. When doing about 35mph+, when I put the engine under load (apologies for my description) its like a dull buffeting sound(whumphumpwhump)/vibration in time with the engine. This has only started to occur recently,
any thoughts chaps?

thanks in advance,
den

Start by looking for inlet or exhause gasket leaks. If this all seems fine then see if you can get a compression test done.

Check your valve clearances very soon.
You find one of them pretty tight.

CharlesY