This is probably an easy one for the experienced, but I'm clueless with cars and hopefully want to sort this myself. 
Fabia MkI 1.9SDi estate. A couple of weeks ago I set off from traffic lights and the car seemed to be misfiring for about a hundred yards, and then sorted itself out. It's not done it since. However it may be coincidence but around the same time I've noticed a distinct lack of power on hills, and I find myself going through the gears where I didn't have to before. I also notice it seems to be using more fuel and the exhaust smells dirty, like a bus exhaust. As I say I'm clueless but I'm guessing it's air filter / fuel filter / glow plugs?

I'm having to resist making the typical SDI jokes here.

 

Does sound like it's overfuelling... a lot. Maybe get a code reader on it and see if anything is lurking before we play that 'lovely' game of parts darts.

Not sure how you can tell if an SDi is misfiring!   I'd agree about the overfuelling, so am going to ask what sort of mileage it's done? This will be confirmatory when we get to a stage when we can do a diagnosis.

It's 140,000 miles.

 

1 hour ago, nevthedigger said:

It's 140,000 miles.

 

By itself it's not a diagnosis, but it does suggest worn injector(s).

Try a bottle of redex

1 hour ago, lewis66 said:

Try a bottle of redex

 

Don't, you'll trigger Sep's 'Snake-Oil Senses'

 

Jokes aside, I'm not much of a believer in Redex either, never found it to be of benefit for any of the fleet.

1 hour ago, lewis66 said:

Try a bottle of redex

Whatever you do don't follow that advice, I did and was on the loo for 24 hours!

1 hour ago, AnnoyingPentium said:

 

Don't, you'll trigger Sep's 'Snake-Oil Senses'

 

Jokes aside, I'm not much of a believer in Redex either, never found it to be of benefit for any of the fleet.

Snake oil?! Fixes everything even slow punctures in my experience! I'd still give it a try first as it's cheap. It definitely worked on a petrol I had once but never noticed much difference on the derv either tbh.