Here's a couple BMW University docs that might be useful:

 

reading through it, very interesting , where did you get these from ?

many thanks for that

-- edit


it says the dme will change increase rev or idle if charging rate is not enough so can it do opposite . it doesn't mention it there but suppose it can .

if the charge rate is too high , it drops the idle to prevent damage ? if so then this answers why my rev is going mad when idle and better when driving . it is still there but not as noticeable .

I guess it can't kill the engine so can't reduce rev . the reason I can not 100% conclude it is the alternator or the theory above is, the rough idle and rev fluctuation also happens when the car is moving so would the ecu really start to mess with rev to protect devices from over current ?

 

Got these over the years from many Google searches

 

further update,


took the manifold apart and cleaned plus changed the glow plug. car is way more responsive now and idle roughness is fixed
i can only assume it was the carbon deposit causing it or glow plug being dead which not allowing the ecu to utilise it to stabilise the rpm.

however the no start is still there. it is driving me nuts and literally crazy . it is something inside the ecu compartment .

I know this because when I remove the ecu relay and plug it back in or play with wires in there , the car starts up again .
so I am only assuming it is to do with something in there.

problem is I have the ecu plug which looks clean, have bunch of fuse which looks clean so literally have no idea of what is causing it .

it could be a weak connection or something. it happened last night after 30 mile journey and as I parked up with battery fully charged, switch off, went to a friend house and pop back in the car and now guess what it is not starting but cranking over.
did try it so much and diffling with ibs and all sort and non fixed it but only the ecu compartment cabling .

I don't want to sell my 6k car for this but really considering it. I have spent so much time on it and can't figure it out.

any ideas please?

would you take it to stealer as I don't think they can do anything ?

 

bump

 

got closer. It seems it is the fuel pump and only happens when the car is hot .

What i realised is the fuel pump is constantly on even when the key is taken off and only way to switch off the bunp is lock the door and a minute later it stops

I am thinking fuel relay sticking, what can it be?




It seems as it is ekp module controlling the fuel and there is no relay. So that may havegone bad. Does anyone know where it is?

 

Do you have the same pdf file for fuel system so can try and workout where the relay is if any?

 

Don't have anything like this. Don't know if it exists or not.

 

any idea if there is a relay or is it the ekp that does it all ?

 

Have you checked crankshaft position sensor?