M70 engine problem

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 unsynchronised 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 commutor 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. Hope this helps.

If it is intermitent it seems like it could be the DME. BMW has a replacement for the DME and both airboxes due to unusual running charecteristics. Check your local dealer, if it is an 07 it should have some sort of coverage, no?

You must have a check engine light on when this happens. Do the test, read
the code and look it up in the charts. It may be a throttle motor, airflow
meter - who knows. go to http://bonnevillemotorwerks.com/techtips... and
find out how to start the code. We can go on from there.

Erik

nice but there are no light's burning anywhereand the throttle motor's work
perfect .
i have read the engine code's already but nothing seems to make the problems
that i have.
the interval service and oil chek meter's are also reset already.
so if there are more sujestions pleace
Jr Kuppers

...

Could be a leaking intake manifold gasket. This is a known problem on the
M70B50 powerplants. Dinan sells a trick replacement gasket.

Paul Michael Brown
Washington, D.C.
Moderator -- E31 owners' e-mail list