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Many owners notice that after a few years the car performs far worse: fuel consumption climbs, power drops, and the idle sometimes shakes. There are broadly three causes.
1. Fuel system problems
A clear loss of power is often caused by poor injector delivery or bad atomisation. Over time this can prevent the engine from starting at all. The root cause is usually insufficient cleaning of the engine's internal system: carbon builds up on the injectors and clogs the needle valve, so fuel is not delivered or atomised properly. The answer is regular cleaning and care of the engine's internals.
2. Electrical problems
These cover wiring and spark plugs. A wiring fault can disrupt a sensor and cause exactly these symptoms. Spark plugs mainly suffer from heavy carbon build-up and ageing, which also cause power loss and can stop the engine starting.
3. Intake system problems
If the intake system is faulty the engine receives too little air, so there is not enough oxygen for the fuel to burn fully. Fuel consumption rises and power suffers.
How does this show up? If the car smokes blue and there is a burnt smell, the intake system is the likely culprit. The usual cause is excessive valve wear or poor piston sealing, reducing intake volume and producing blue smoke.
All of this comes back to insufficient care. To keep performance and restore power, look after the engine's internals and keep the fuel path clean: clear the carbon and prevent the blue smoke before it starts.