Hi, firstly, at 10000km it hasnt even reached 1st service (20000). But its been around a while. I wonder if it has had the tps replaced under warranty as thats what it sounds like.
DONT let anyone go changing the idle screw settings. Contact a yamaha dealer who can look it up for you maybe.
The tps can be checked with a multimeter but it is a little fiddly to get to. Its on the exhaust side behind the engine cover.
Not an expensive item. Dont go fiddling with everything else!
See what others here say but I would reckon thats your first thing to check.

Thanks a lot for helping!
Both the Dutch and the Brazilian service manual have services listed on 1k, 10k, 20k etc. (every 10k). But for this case that doesnt really mather i think. What i know is that the bike has been stored for several years.
I passed your sugestion about the TPS sensor on to my mechanic, and also told him to leave the ajustments of the injection untouched.
In case they need to replace this sensor, is this an universel part, or has each brand/model a specific sensor?