I'm not at home now so I ain't sure but I can check the script later. However, I think it was something like:
? !(isengineon _whatever) : tjommitjommitjommi
This checks if engine is off on the vehicle _whatever, thus the !, which I think you know means Not.
So if you want to wait untill vehicle has his engine on and then, say, put a hint in you do this:
@ (isengineon _whatever) : hint format ["%1 just put his engine on!", _whatever]
Happy cutscening (like your cutscene page btw)
:beat: *Gets Shot* :beat: