The simplest answer is that the engine’s idle speed is set too low. I think these engines used a stepper motor to control the throttle at idle, and if this fails the engine will run with some throttle applied, but will stall at idle.

If that’s not the cause, you need to look a bit deeper into things like fuel pressure at idle and whether there’s some kind of problem with the fuel-injection system. It could even be something as simple as a dirty fuel or air filter. A good mechanic will know how to alter the idle speed to prevent this happening, although it may involve a new stepper-motor unit.

A dirty or clogged fuel filter will stop a modern turbo-diesel engine dead in its tracks. In fact, it’s one of the first things a switched-on mechanic will check on vehicles like yours. So if the mechanic has changed the filter and restored to car to full health, then I reckon he or she has probably nailed the cause and fixed it very simply and cheaply for you.

Let’s be honest; there are literally thousands of things that could go wrong that might make your vehicle stop. Modern cars are very complex things, but you need to have faith that sometimes, simple problems occur and can be fixed simply.

Running on after the ignition is switched off is more of a problem in petrol engines than diesels. But you haven’t told me which engine your Triton has, so maybe it’s the 2.4-litre petrol we’re dealing with here. If so, you may find that the running-on is being caused by poorly timed ignition which could suggest a problem with the physical bits that make up the ignition system, or even a problem with the computer that controls it all. Worn or leaking fuel injectors could also cause this problem.

If your engine is the turbo-diesel, then another potential cause of running on is a worn or stretched timing chain (the petrol engine uses a toothed timing belt which shouldn’t stretch) that has allowed the camshaft to get slightly out of phase with the crankshaft. In both these cases, the fault could easily be enough to trigger the check-engine light and keep it on to alert you to the problem. Have the vehicle scanned to see if there’s an ignition fault or what’s called a camshaft deviation, indicating a worn timing chain.