Buddy, I have another suggestion for you.
I did the following jobs on my vitz after its fuel efficiency dropped and rough vibrations on idle appeared:
Cleaned Throttle Body
Inspected Fuel Filter (located in fuel tank): This job proved to be needless as the filter was found clean.
Cleaned MAP filter (located behind throttle body)
After these activities, the rough idle problem got solve. However, no improvement in fuel average was observed.
Then after 15 days, I reset my ECU settings by disconnecting battery +ive terminal for 1 hour, and then reconnecting. Viola!! It worked wonders... All of a sudden I started to get additional 3 kmpl than previous.
For these modern cars, it is important to give ECU a refresh after cleaning jobs to witness improvement.