The engine management light on my astra 1.7tdi is pretty much permently on, but van is ok. Every now and then it coughs, loses power and dumps a cloud of black smoke. Then power comes back. Help???

"Is used everyday and it very reliable" --- well maybe except for that coughing, power loss and black smoke cloud part... Get the codes read and find out all the reasons that are keeping the engine management light on. Write the code down. Come back on here and publish it. We can suggest cost effective repairs to keep your Astra purring.