My 53 gt tdi is a swine to start and more so when cold. I have changed the glow plugs, and was then told to change the coolant temp sensor. Doing this made no difference at all. Was then told to disconnect it and try starting. Disconnected it and the car burst into life like when it was new. Reconnected the sensor and it wont start again. A VW mechanic has told me this is down to a fault in the ECU sending the wrong signals. Can any one suggest anything else before i spend a fortune on a new ECU?