97 avant 2.8

 

So, your 1997 A6 Avant 2.8L 12 valve AFC engine only runs with the crank sensor disconnected. By disconnected, do you mean at where it plugs into the wiring harness? I got the BentleyPublishers.com Audi shop manual CD that covers your car. You need to get an OBDII or VAG-COM scan, to see if there are any stored malfuction codes. I never had this happen, so without the codes it could be almost anything, even bad wiring or the crank sensor. You can go to an auto store for a free OBDII scan, however it will probably show that the crank sensor is not working, since it is dissconnected.
You need to give more information, such as why you disconnected the sensor.Did you install any aftermarket modules to the engine?