Alfa Romeo Repair: Very unstable idler wheel & RPM growing, rich fuel mixture, alfa 2

Question
Dear Mr Sokol!
I have an Alfa 2.0 TS 1999 (total 200 000 km).
Please give me any idea about the origin of very unstable idle wheel, click noise and the worst - very unstable growing of RPM with car jerking. The (new) spark plugs&catalytic converter are black inside but the engine have not any lost of oil - after 2500km from the replacement (Areca 10W50) - the same level.
Is this only the variator problem?

Answer
It could be the cam timing.  What you are indicating is a very rich fuel mixture.  You might check ignition timing and fuel injector condition before doing anything else.  A faulty fuel injector can give a metallic click as well as shoot a stream rather than a vaporous shower of fuel.  This will cause a lot of unburned fuel.