BMW Repair: 1994 318i check engine light, oxygen sensor, knock sensor

Question
The check engine light comes on after a few minutes of running and then goes off whenever it wants to or when you take your foot of the accelerator.  I checked the fault code with a Peake R5-fcx and it read "CF" which according to the manual is "knock control regulation".  I had a tune up done as well as a fuel filter, and oxygen sensor and three belts replaced.  This did not solve the problem.  Also, when the car is warm and gets parked and shut off to run into a store or something, when I restart it it runs for a split second then the battery light comes on and the car dies unless I apply the accelerator.  Any advice would be greatly appreciated.

Answer
Joel If the car doesn't restart when hot without pushing the accelerator I usually run into a carboned up idle valve. I am not as experienced on older vehicles so I don't know. Make sure the knock sensor wiring is good. You could try a knock sensor.
-Evan