Thanks for sharing and good to know.
The timing chain is another source of problem for de-pollution fault. Read from other forums including BMW-MINI that the tensioner and chain guide can wear down and become loose after a while. The so-called death rattle; my neighbor has the Mini and everytime the car is started, it makes a horrible scrapping sound for 1-2 secs. Our Pug has the same start-up sound but much-much softer.
Decarbo is short for de-carbonising. It means to clean the engine from carbon deposits. 2 ways
1. To spray into the intake some petroluem based cleaner while revving the engine.
2. OPen up the engine, dismantle the "head", remove the valves (injap) and scrape out all the carbon/gum/sticky oil, grind the valve seat and re-install the engine with new gaskets.
Of course #2 is permanent way but more labour time and parts required. And to be done with correct tools. I will only open up the engine at last resort because once this is done, the engine never feels the same again. This is like major surgery being done.
Root cause: EGR + Direct Injection leading to excessive carbon buildup around INLET valve.
As exhaust gases are leaving via the exhaust valve, a small portion of the hot, dirty exhaust gases are re-routed by EGR back into the inlet valve. This hot gas is not cooled down by any cooler, unlike in VWs where there's an EGR cooler.
The Peugeot's EGR system cannot be removed from the engine...unlike on locally-assembled Putra and Satria GTi's glorious 4G93 twin cam engines.
As the hot dirty gas mixes with fresh air-fuel mixture and enters the combustion chamber, carbon builds up very slowly around the INLET valve. When build-up becomes excessive, the carbon becomes red hot and starts igniting the airfuel mixture thus causing knocking. That's when you get that warning message. At that moment, to "save" the engine, the ECU instructs all injectors to go into max duty-cycle mode pumping in loads of fuel to cool things down, and ECU retards ignition timing....sudden loss of power, but engine is safe.
Pouring injector cleaner or similar products into fuel tank won't work because since its direct injection, the injectors are spraying straight at piston top....it cannot spray upwards towards the roof of combustion chamber (where the valves+carbon are situated).
Hence, the only way is to perform manual cleaning of the valve area. Using machines that pump in detergents might work and I've heard of one guy who can do a decent job, but don't have his contact details.