It sounds like there’s either a problem with the throttle pedal, the throttle mechanism itself or, most likely, a glitch in the communication between the two. Instead of a throttle cable directly linking the pedal to the throttle, modern cars use what’s called fly-by-wire. In this case, that means a throttle pedal where input is converted to an electrical signal, which is then transferred by the computer to the throttle telling it to open. If there’s any wiring or software problem within this system, you could easily experience this sort of problem.

You’re quite right, too, that this represents a very dangerous situation. Many crashes have been caused by a following driver assuming the car in front was about to take off. And when, for whatever reason, it doesn’t…

If the computer won’t tell you what’s happening, an auto electrician should be able to take readings from the throttle pedal and the motor that actuates the throttle itself. From there, they should be able to discern which component is not playing the game properly.

You could be looking at an engine that has a fuel-system problem. A lack of fuel pressure or volume (or worn injectors) can play havoc with a turbo-diesel engine at higher speeds thanks to the higher loads being placed on it. You may also have a worn or damaged turbocharger or perhaps an inlet manifold that is partially blocked from fumes and soot that are part of the vehicle’s emissions system. The problem could even be due to a blocked DPF in the exhaust system which could require manual cleaning or even replacement.

But this is another example of a car that’s still under warranty being the responsibility of the manufacturer to put right (provided the vehicle has been serviced correctly). Give the dealer very chance to fix things, but if they throw their hands in the air, then Kia Australia’s customer service department is your next stop.

There could be something wrong with the vehicle that is causing engines to blow up, and simply fitting a new engine is leaving it open to the same catastrophic problem(s). A fuel supply or cooling system problem would be just a couple of possibilities and fitting a new engine to a vehicle with such a problem could easily lead to successive blow-ups.

There’s also the possibility that you’ve simply been unlucky. Was the second engine a used one from a wrecking yard or a rebuilt unit? If it was the former, you might find that it was just about ready to expire, and the fact that it was fitted to your vehicle was not a factor. This is why it’s always important to have any second-hand engine tested before it gets fitted. Good quality used engines will come with a written report to prove there’s some life left in them.

There’s also the owner’s approach to a new engine. Were you careful to check the oil and coolant of the new engine once it was fitted and running? A second-hand engine might have an oil consumption pattern you’re not familiar with, and ignoring this important check could see it run dry and expire. Not pointing fingers, but even a 'new' second-hand engine requires a close eye kept on it.