2022 forester wilderness

[dehavenscott]

took in for service was idling rough one cylinder has excessive carbon build up on the piston they have had it 2 weeks trying to removes the carbon and it is still idling rough cannot figure it out have opened an inquiry with a field engineer has anyone else had this problem

 

[Dick Foster]

No but I would do a compression check, to try to see if its a top or bottom leak, ie the cylinder valves or rings, after first checking cylinder ignition plugs wires the coil packs etc. It's could even be an ECU problem, but that would be unlikely. Ask them what they have done, in case it's just a dumb tech.