First, since the car is fairly new to YOU... I would set the valves and change all the fuel filters... just on principle...
And do the "Diesel Purge" treatment with two bottles... at $20 , done at the time of the fuel filter changes this is good base line establishment....
The combination of things you have mentioned sound more like fuel related than piston rings/ valves... which is good news...
Check to see what idle adjustments are availble on your car ...