Car: JDM Lancer 2006 4G15 Mileage easily above 220K km. No overhaul done, the car is not consuming oil only a minute amount in 3k km OCI which is ignorable.
Parts replaced since I own it: Both oxygen sensors, all the belts, injectors cleaned and all the basic maintenance. Plugs have done 20k km's and 3k km's ago when checked they looked healthy. Plug seal that is on the inside of the valve cover one of them seemed damaged and oil had reached into the plug not sure if that could cause significant issues. Tappet adjustment was done based on workshop manual and valve seals were also replaced. The car does not have any issues of coolant drinking either or oil seeping into the cooling system.
I know the history of this car, coils, distributor or any fueling related part are still original except for brand new oxygen sensors imported from USA.
Now right after a throttle body cleaning session the idle issue where load was not accounted for was resolved but the car started jerking and sort of missing in low RPM, this is true for both cold and hot. Because it is a cvt I have to deal with this till 80km/h because the rpm hardly climbs out of the low rpm situation due to the endless gearing system and it seems a very weak car with constant jerking till it exceeds the low rpm situation at around 80km/h where it becomes normal. I have to start in L and Ds to exceed that low rpm where the car is missing and has extremely low power, this is most pronounced on a feather throttle which was enough to send the car to 80km/h previously. Full thorttle on L and Ds starts with missing but once in high rpm it acts as it should.
I would like to know what parts should we be looking at diagnosing when I take it to someone? Because to me it seems the whole fueling and ignition system will need to be checked