Motors can do very strange things.
Sometimes mine will idle at 500rpm, sometimes, 1000rpm, sometimes 1500rpm.
Sometimes it starts perfect cold, sometimes it will idle at 300rpm flick the throttle go up to 1500 as per it should, sometimes it will come back down to 500 after i flick it up to 1500.
Faulty injectors are quite common for a motor that hasn't been run in a few years.
I'd get them cleaned purely for piece of mind.
You don't want one injectors to be down 20% and melt a piston do you?