750i running on 6 cylinders

Don't let the fact that it is intermittent throw you off the trail, it still may be the throttle bodies as I found with mine. Here is what I posted for another similar question:- The on board computer does a "roll call" across many sensors before starting. If it gets no response, or an unacceptible response from any of the sensors is can put the car into "limp mode" shutting down one bank of cylinders, and only delivering a small percentage of available throttle. The theory is that you can "limp" back to the mechanic. The most common cause of this is a poor or un-synchronised response from the throttle body (AKA DK Motor) sensors. The M70 has two throttle bodies, one for the left and one for the right bank. To run efficiently these need to open and close in unison, like a mirror reflection. Wear, or more commonly accumulated dirt, in either of the DK motors can prevent them from performing in sync. BMW service manual lists the repair procedure as "replace" but that will cost between 2 and 5 thousand dollars depending on where in the world you live, plus labour. I chose to strip mine down and clean them out myself, cost $0. There are some great links on the web showing how this can be done. Hint - there are two chambers in the DK motor, the commutator drive chamber and the throttle position sensor chamber. I would advise only cleaning out the commutator area, and see how it works. If you choose to open both chambers, be very careful not to bump or move the position sensor, and if you must, take careful note of it's position first. Note the sensor arm is a "friction fit" not a spline or "D" shaft design, which means it can be freely rotated around the shaft using the fingers, leaving you with no way to navigate back to the original position. - Having one or both sensor arms "almost" in the right position can cause the EML warning to be intermittent. Hope this helps.

The other bank has been shut down due to a fault. I'm no expert on the
V12s but I think the motor that controls the throttle may be faulty. Not
cheap.

Third actually. Often due to a bad supply voltage to the gearbox. Can be
caused by dirty wiring, bad battery, bad voltage regulator (on back of
alternator).

These problems all smell electrical. I think the first thing you need to
do is springs clean the wiring. Open every connector and use abrasive
such as wet and dry paper to get all the contacts nice and shiny. Same
for the battery terminals and all te body grounds. Don't forget the
connector that plugs into the gearbox. This sort of thing helped a lot
on my 635. Dirt on the contacts causes high impedance and can lead to
lower voltages at the other end of the wire.

On older BMWs you also want to think about changing some of the relays.
They've been working hard for 13 years now! Think about new Motronic and
fuel pump relays, normally about 10 GBP each.

--
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Email: , John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
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Please don't. Many connectors are plated to help prevent corrosion, and
removing the plating will make things worse. There is no need to use an
abrasive as proper chemicals will dissolve any corrosion. Use a good
quality contact cleaner followed by contact grease to waterproof and help
prevent further corrosion. In the UK, Electrolube products are my
favourites. From any good electronics supplier - even Maplin. ;-)

--
*If work is so terrific, how come they have to pay you to do it?

Dave Plowman London SW 12
RIP Acorn

Where do you get contact grease? I've tried and I can't find it. I don't
even know what it's made of, just that I used to have a tube and it was
called 'contact grease'.

One source would be http://www.carcareonline.com. See
http://www.carcareonline.com and
http://www.carcareonline.com
Richard
...

Maplin RE 90 2.99 for 50gm tube or RE81 3.99 for 70gm aerosol - made by
Servisol.

--
*Did you ever notice when you blow in a dog's face he gets mad at you? *

Dave Plowman London SW 12
RIP Acorn

Damn them. I've asked in the shop at least twice and got nowhere.

Thanks both of you, I should be able to get some now.

To be fair to the shop assistants it's just called silicon grease in the
cat - you have to look at the description to get the full info.

--
*Before they invented drawing boards, what did they go back to?

Dave Plowman London SW 12
RIP Acorn

Aha. Well, I've got some then. I thought that might be it but, having
bought some, did not dare use it in case it wasn't. :-)