Noticed jets of soot on the ground or against the wall when firing up or even about to turn off. If I'm giving it some then get a cloud of smoke (though not thick and black) from where I was!
Is it likely to just be burning a little rich???
Only just passed emissions too -had to really rev it up before testing!
Could it be anything else?

 

is the cat removed?

 

I have a sports cat for emissions but even then just managed a pass!

 

From the title I thought you`d found.....

 

 

What year it? Uk/JDM?

Uk Classics were renowned for running rich which when on fully throttle at high revs (well, until the MAF dies ), quite acceptable as it stops it detonating.

The soot is more likely just from consensation (water) picking up bits of soot in the exhaust system and dumping it out when you fire it up.

 

It's a Type25, 2.5 cosworth. Keep missing Iain so thought to ask Scoobynetters...never failed yet!
It's got a cold map so definitely rich on starting and I know it runs a little rich anyway but seems like its more than usual......perhaps it is because of the extra condensation in this weather...

 

Lambda sensor might be on it's wway out, is it using more fuel?

 

Hard to be sure. It gets very mixed drives of fun and general/commute. I think possibly. Presumably that would show up when plug the car into a computer?