The crankcase breather valve and its four lines often fail. The valve sticks open and the lines break, and both let false air in. The valve and the lines last between 110,000 and 200,000 km and typically fail around 150,000. In cold weather the fault develops faster, because the condensing vapour freezes in the valve and blocks it. The symptoms are oil being used up, a rough idle and blue smoke, and a dense vapour can also appear at the front under the bonnet. If the drain of the valve blocks, the burnt oil mist also leans out the mixture and the engine fault light comes on. Left untreated it can end in engine damage. There are two tests for it, and both can be done at a viewing. With a warm engine at idle, lay a flat plastic bag over the oil filler opening. If the bag stays up or is only drawn in by 2 to 3 cm, the valve is fine. If it is drawn in strongly, the valve has stuck open. With a cold, stopped engine take the breather line off at the front corner of the cam cover and blow into it: you should hear bubbling in the sump. If you do not hear it, one of the lines has broken or the drain in the dipstick tube has blocked.

The DISA valve is the black box on the side of the intake manifold, and it adjusts the length of the intake so that there is more torque at low revs. The shaft of the valve breaks at its base, and then the flap falls off: the pieces can get into the engine and cause major damage there. Its membrane can tear separately as well. The symptoms are juddering on acceleration and a noticeable loss of power, and the valve can also hiss loudly after the engine is switched off. The seal of the intake connection is cast into the DISA, and as it shrinks it lets false air in. Its condition can be checked with the valve removed. The flap has to turn against resistance, spring back when released, and have no play. With the vent hole at the bottom of the round valve held closed, a flap moved by hand may only spring open to 45 degrees and then has to stop. With an aftermarket DISA the experience is that the trouble is back after a year, so a repair kit or a reconditioned factory part is the better choice.

The seals in the camshaft adjuster (VANOS) age, and the rattling noise is most noticeable from cold, right after starting. The noise fades or disappears as the engine warms up.

In the ZF six speed automatic (BMW codes GA6HP19Z / GA6HP26Z) the electrical connector of the valve body control leaves the gearbox housing through a plastic sleeve. That sleeve and its seals age, and they let oil through.

The impeller of the belt-driven water pump is made of plastic, and if the blades break apart, there is nothing left to circulate the coolant. The belt keeps driving the pump, but the engine gets no cooling and heats up quickly.

The VANOS solenoid valves fail sooner or later, and that gives fluctuating revs and a noticeable loss of power at low rpm, sometimes starting trouble as well. The valve itself is not always the fault: the contacts of the connector can widen or oxidise, and then there is no proper contact. An aged camshaft or crankshaft sensor can cause the same. Oil can seep along it into the wiring harness, and capillary action carries it towards the control unit. From there a VANOS fault code, a lambda fault and misfires can follow. A widespread misconception is worth stating here. The rattling heard on a cold start is NOT an indication of the condition of the VANOS: the noise comes from the play in the needle bearings, which every VANOS has, only not every drivetrain resonates with it. Anyone who concludes the VANOS is fine because it does not rattle is concluding wrongly.