The air suspension fault light is on permanently on and suspension hard on my XJ8 2004
Once I start the car the car lifts to the highest point and the suspension is hard all the time.
When the engine is switched off the air is released out the front of the vehicle in a burst of compressed air and the suspension then lowers down as low as it can with wheels almost touching the wheels.
Any ideas why this is happening and what the solution is.

 

Andrew, sounds like one of your suspension air solenoids is failed and it is pressurizing one/pair of air shocks and the car is compensating by raising the other corners to match. The best advice that I can give you is to get your hands on a dealership level computer (ie, an SDD computer) and go in and look at the error codes associated with the suspension. You should most likely see an error code relating to one of the solenoids. At a minimum, it should say "unable to control XXXXX corner of the car" (or something to that effect). That will then atleast give you a starting point of where to start the search. I would suspect that the issue is in the front end of the car because of the burst of air that you get. But, not knowing your year of car very well, I am making a logical leap.