These are fully repaired and calibrated Econocruise speed control modules. There are two main reasons why the cruise control function on an XJS or Series 3 XJ does not work – either the throttle actuator bellows needs re-sealing or the electronic module has failed. If, after activating the cruise control switch, the engine speed slows or speeds up instead of stabilising at the set speed, then you have a faulty module. If nothing happens at all then either the bellows is leaking or the module is faulty. These modules suffer from ageing components which need to be replaced, and then the unit re-setup on a test jig. We have all those facilities, and a great deal of experience! We can also repair your own module, though that is not necessarily cheaper. We also offer a repair service for the vacuum bellows unit, to include cleaning the two solenoid valves, and re-sealing the bellows.