Many cars don’t appreciate having the brake and throttle peal pressed at the same time. It’s partly a response to cases of pedal error in the USA many years ago that almost bankrupted some car companies via legal cases brought by owners who had pressed both pedals and had their car rocket through a wall or into a shopping centre. The US courts called it Unintended Acceleration. The rest of the world called it Pedal Error.

In any case, if you do press the brake and throttle pedal together, the throttle may – as you have noted – become unresponsive. But it should return to normal operation within a few seconds. You claim not to be pressing both pedals at once, but sometimes, even a light, unintentional brush of the brake pedal is enough to send the car into no-throttle mode.

That said, you could have a vehicle that incorrectly 'thinks’ you’re pressing both pedals when you are not. In that case, the sensors that detect pedal pressure may need to be changed. You could also be dealing with a car with a faulty body computer – the brain that links all these functions together cohesively.

It kind of all depends on why you’re considering changing the wheels and tyres on your vehicle. If it’s for aesthetics, then go right ahead, but bear in mind that ride quality will likely suffer as a result. That’s because an 18-inch tyre will (typically) have less sidewall depth than a 17-inch tyre. And a tyre’s sidewall plays a huge part in how a car feels to ride in. Fundamentally, the smaller the sidewall, the harsher the ride will be.

In an off-road sense, you’re probably better off sticking with 17-inch wheels, too. By fitting an all-terrain tyre, you’ll improve your off-road grip. That said, all-terrain tyres (once restricted to smaller sizes) and now available in 18, 19, 20 and even 21-inch fitments.

Most of the references I can find regarding the 20-14 Jeep Compass with the 2.0-litre petrol engine suggest that it requires premium unleaded fuel with an octane rating of at least 95 RON. Given that the engine has a fairly high compression ratio (one of the factors for requiring PULP) of 10.5:1, that’s not really a surprise even if the output of 115kW doesn’t suggest a highly tuned engine. I’d be inclined to take the Jeep dealer’s advice and use premium fuel. Engines tuned for PULP can suffer internal damage if they’re run on an inferior grade of fuel.

The other question is why there is a discrepancy between the handbook and the dealership. The advice to Compass owners in the US is to use low-octane fuel (as low as 87 RON) where possible. This is possibly because the engine uses a different state of tune on the US market. One guess, therefore, is that while the Australian version of the Jeep requires PULP, the handbook hasn’t been changed from the US version to reflect this.