[ozi jim]

You are not thinking it through.
You scanned and none of the sensors came up as an issue, you have to trust that and move on.
An ECU will throw an internal error code or a bunch of codes that make it a liar.
If you think its an alternator then when it starts to missfire remove the fan belt if its causing any RF then that will prove a point, if it aint turning it should not be an issue.
I assume the alt is charging and battery is full.

I would be very surprised if its an ECU.
Only time I have seen BMW ECU fail is water.

Is this engine fitted with an ignition module.?????

It sounds like an ignition module because that will cause the rev counter to flick,the counter circuit is linked to the ign coil primary circuit, and so is the module and the primary side of the ign coil.
And also will stall when put under load because the circuit is failing.
Ign modules are matched to the coil, I gather you put a different coil on it (from the auto store) non BMW this can cause the module and or coil to fail if there is a miss match.

Before you do anything you should change the coil and module.
You said the coil is new but if not suited to that module they only last a week or two.

Why did you change the coil originally ??????? was there a problem.


jim