Toyota NR (1NR / 2NR)

Toyota's 1.3 with Dual VVT-i on both camshafts — in the Yaris, iQ, and Daihatsu's Sirion and Xenia. A small, chain-driven, port-injected four built for economy rather than for anything else.

Because it is port-injected there is no intake-valve carbon, which is the single most common modern diagnosis and does not apply here. A rough-running NR is ignition, fuel delivery or a vacuum leak, and the diagnostic path is the straightforward one.

The variable-timing solenoids and their oil-control valves are the recurring item. When one clogs the engine sets a timing code and loses response, and on an engine this small the loss is obvious to the driver. It is an oil-condition problem far more often than a failed part, because both phasers are hydraulic and run on whatever is in the sump — and these cars are cheap, often neglected, and driven short distances.

The water pump is the other item that arrives with age. Otherwise it is unremarkable and long-lived, which is what it was designed to be.