I can see that your pretty sad with the Vehicle your having.
This is not a premium Sedan/hatch anyways and to target that much Range customer Toyota produced this car in that price range however those build quality failures are shocking.
Lets see what you CAN do to fix some of the issues
- Engine Idle problem can be solved. Try cleaning the engine injectors, replace spark plugs , engine oil, oil filter, air filter and clean AFM sensors. Use 98 octane fuel once in a while . Set the speed.
- Vibrations: If engine is vibrating too much Add Strut bars in the engine bay
- Engine noise coming inside : Check for the seals that is between car engine and the interior. that is wire holes etc etc. This can be eliminated
- Gravel road noise: I heard this happens to most of the small car. Two Reason: hollow shaped alloy wheels and other is the car mats .
I would suggest you to take out seats and the middle dash and remove the carpet. Put a fine layer of high quality foam that can soak that noise.and put back on the OEM
mats on top.
- Air con smell: Try switching the AC from Outisde air to inside and see if problem persists. IF does . Then go check your CABIN filter.
Normally they don't put any filter in cabin filter box. make one your self or clean if there is one already.
- Paint cracks: Use paint protector and regularly polish the car like once every fortnight.
Hope that helps