We had that 2 times on an E32 750 Alpina B12.
First time the ground cable from the engine to chassis was bad. That we replaced and idle was stable.
Second time the return line from fuel tank = fuel tank breather line and the valve were defective/broken. See here on the B12 http://e32b12.blogspot.jp/ click in the index on idle and scroll far down.
That is the system on a M30 http://www.realoem.com/bmw/enUS/show...diagId=16_0112
17 Fuel tank breather valve BOSCH 13901711395
The tank breather valve should have a resistance of 45 ± 20 Ohm and should be closed without power.
others:
idle control valve
throttle valve
But as the car has EML, this can be neglected. How about the vacuum hose under the intake? http://i1275.photobucket.com/albums/...psdqxehvrp.jpg
http://www.bimmernut.com/forum/showt...llo-from-Spain!
http://www.bimmerforums.com/forum/sh...nifold-gaskets
http://blog.bavauto.com/8393/bmw-m30...i-635csi-735i/
Just found a thread on the German forum, there it was the DME http://www.7-forum.com/forum/5/m30b3...-a-167325.html
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