Smoking

My 635 seems to kick out a lot of smoke when it is first driven after being started from cold (overnight etc).

There's no real smoke when you start the engine, but as you pull away, it kicks out a fair amount of dark grey/black smoke. I don't think it's oil (it's not blue smoke, and the car doesn't seem to be using any oil).

I'm assuming it's some sort of rich running problem - it only happens when the car is first driven - after that it is fine, and doesn't smoke under hard acceleration or on the overrun.

What should I be looking at?

Yes that's about the strength of it. If the engine isn't really under load (car stationary after cold start) then blipping the throttle will produce a cloud of smoke. This will happen repeatedly (I generally don't like prodding the throttle when it's in "P" or "N" because mine's an auto and I have heard rumour that it b*ggers up the clutch on the autobox).

As soon as I pull away, another cloud of smoke and then it's gone. Almost like the DME is re-tuning the mixture after I pull away or something. I have got a non-standard air filter (K&N) which I did think might be confusing the DME computer or something. 

I would try some injector cleaner first - generally advertised in TBMW & BMWCM.

Then you could look at the cold start gizmo - that might be sticking.

I'd go with brucey on this one.  The valve stem seals get hard with age and allow oil into the combustion chamber.  It's a common problem on old BM's

Head off job to change out though

Otherwise just learn to live with it on start up.  It's no big deal

In my M635 I booted to 100mph in 3rd and then let it engine break down to 60mph.  Tell tale puff of smoke out of the exhaust as the engine went into max vacuum.  A dead give away for worn valve stem seals or worn rings.  Oh my god did I say worn rings!!!!!! - unlikely but possible.

Ian

probably not, unless your box locks up above a certain engine or road speed. My 4-HP22-EH box will  overrun a bit in E mode above 60mph, or in S mode at other speeds (in a way I have not yet figured out). I guess you'll have to try it out.

BTW oil burns bluey grey if it is burn hot, but anything burnt too cold will tend to burn black, even petrol; this is why cold plugs soot up on short runs.

Cheers