Finally was able to get the japanese text that tyrone mentioned, translated... and yes it does mean:
"Don’t pour water on the engine bay due to risk of short circuiting after ignition"
So, Tyrone, the earlier rough translation was also correct! We should use water sparingly and very carefully, if at all.
Regarding throttle body cleaning, it is only needed when the car is giving trouble on idle. A dirty throttle body causes problems at low rpm... e.g. when u move your foot from the acclrtr to the brake in normal driving, the engine might stall while rpm is decreasing! Other problems are mostly due to other things. Also, while cleaning throttle body, ensure the spray or cleaner is safe for the cat converter - else you know what will happen.
congratulations and good luck. there's plenty of checklists available on internet as well as this very forum, though u'll have to search for it. i remember posting one myself.
u'r right, max speed should've been more. but there are many other causes possible. e.g. the weight you're carrying, facing wind, tyre size and alignment, etc.
internal causes possible (in order of likelihood and ease of fixing):
dirty air filter
malfunctioning or dirty MAF sensor
dirty fuel filter
partially blocked cat converter