CTSA engine faults.

The crankcase breather of the five-cylinder 2.5 TFSI leads the oil vapour into the intake, and the stub of the diverter valve sits directly next to it. When the diverter valve opens on lifting off, it carries the oil vapour along, and the vapour condenses in the air filter housing, because the stub is right in front of the housing. The oil therefore collects on the filter element and in the bottom of the housing, the amount grows with use, and under load oil mist comes out of the intake pipe as well. The consequence is twofold: measurable oil consumption, and oil reaching the intake speeds up the carbon build-up on the intake valves, which is already heavy here because of the direct injection. This is not a broken part but where the line runs, so it shows up around 40,000 km already, and earlier on a car used hard. The repair is rerouting the breather or fitting a catch can, 200 to 600 euro.

With direct injection the fuel does not wash the intake valves: the petrol goes into the cylinder, not behind the valve. The oil mist and soot arriving through the EGR and the crankcase ventilation therefore build up on the valve stem and head, and from 80,000 to 100,000 km they restrict the flow. Symptoms are hesitation, loss of power, a rough cold start and misfire. It is not a part failure: it is a consequence of the design, and therefore it comes back. Cleaning (walnut or dry ice blasting) helps for a few tens of thousands of kilometres.

The G62 sensor tells the engine control unit how hot the coolant is. If it is faulty, the control unit thinks a warm engine is cold, and runs it rich: hard warm or cold starting, a rough idle, markedly increased fuel consumption, and a dash temperature gauge that jumps around or never reaches its usual reading. The part is cheap and can be replaced in half an hour: the trouble is that many people do not recognise it and replace an injector or a lambda sensor instead. If the fault persists, the rich mixture can destroy the catalytic converter too.