@ nyari,Kwani your car does not have a bonnet?
I have used my car almost every for three years without ever washing the engine and it is very clean- The only cleaning is the wipe by my mechanic after oil change to get rid of the spill. or you are the kind of people who want to race like Safari Rally drivers in mud.
If you insist,wash it and I dont believe your d4 (Premio or Rav 4?) can come near the GDI in terms of comparison.
For the juddering of your car on hills,if its an autiomatic,the likely place to check is the gearbox. Could even be a loose panel but at the worst could be a slow knock.
But because you want to save say 3-5K on diagnostic,choose the one which sounds best to your ears and wish you luck.
Everyday!