Presage knocking combustion

Sounds like you've got detonation. That knocking noise is the fuel-air mixture exploding unevenly in the cylinder. A few things can cause it. Have you tried running higher octane fuel? Sometimes that helps. It could also be a faulty knock sensor not retarding the timing when it detects pre-ignition. Or worse case, carbon deposits building up in the combustion chamber, raising compression and causing the fuel to ignite too early. When was the last time you had the engine tuned?

Higher octane, huh? I usually just get whatever's cheapest. And engine tuning... hmmm, good question. It's been a while, like, years. What exactly does engine tuning involve, and could that really be the cause of all this mess?

Yeah, running lower octane than recommended can definitely cause knocking. Engine tuning involves checking things like spark plugs, timing, and air-fuel mixture, all of which can contribute to your issue. Carbon build-up is a real possibility given the symptoms, especially with that mileage and the age of your Presage. It could be worth having a workshop scope the cylinders to check for carbon deposits. Detonation can seriously damage cylinder heads if left unchecked.

Okay, thanks for the advice. I bit the bullet and took it to a local workshop. Turns out, the knocking combustion was indeed caused by deposits in the combustion chamber, just like you suspected. They cleaned it all up, and now she runs like a dream - well worth the 425€!