Mitsubishi Colt Engine Problems

You've got no recourse to the dealer or to Mitsubishi, the car is seven years old, and the problem you've got is fixable and shouldn't be expensive. The most likely cause is a failed sensor or a wiring issue, it is most unlikely an issue with the transmission of the main ECU.

Mitsubishi's recommendation is for fuel-injected models only, so I   would not use E10 in your wife's car. It would be best in your   circumstances to go to the higher octane petrol.

This is an older car now, and although it’s a simpler device compared to most newer cars, there are still thousands of things that can go wrong and cause a loss of performance. A full service and tune would be the first thing to do, as you may find the car is simply not running as well as it should be due to blocked filters, old spark plugs and possibly even stale fuel. A service and tune will rule out that sort of thing.

From there, you need to work out whether it’s the engine that’s the problem, or the transmission, or a poorly adjusted park-brake, or even something in the chassis like a binding brake or perhaps under-inflated tyres. All these things can make a car feel sluggish.

If you (or your mechanic) do decide that it’s the engine at fault, don’t rule out things like a blocked exhaust system, a dud sensor that controls the fuel injection or something simple like a vacuum leak as a result of a missing or burst rubber hose.