Mitsubishi 4A9-series (4A91 / 4A92)

Mitsubishi's small petrol four — in the Colt, Lancer, ASX and Xpander.

It replaced the long-running 4G1 family and is a lighter, all-aluminium design with a timing chain rather than a belt — which removes the single most expensive scheduled item those older engines had.

Its recurring complaints are ordinary and cheap. A rough idle that clears as the engine warms is very often the idle air control or a vacuum leak rather than anything internal; the ignition coils fail one at a time and give a misfire under load first; and the timing chain tensioner rattles briefly on a cold start at high mileage.

The variable valve timing depends on oil pressure and cleanliness, so a flat top end or a rough idle on a neglected engine is an oil question before it is a mechanical one — the same rule as on Honda's i-VTEC and Toyota's lift-cam engines, and for the same reason.

It appears in cars sold under other badges in several markets, which is worth knowing when the model name finds nothing: the engine code is what to search.