irratic idle 1983 xj750 seca

Hello i'm new here.

i have a 1983 yamaha xj750 seca. bike runs great but been having a problem with the idle. sometimes it idles fine. But other times it will idle up to about 4000rpm and stick up there and slowly go back doen or just stay there.

I've tryed adjusting te idle screw but that doesn't help any because then it is just to low and the bike dies out. I've tryed spraying all the boots, and everything to check for air leaks but found no difference in idle when everything is sprayed down. and i'm just at a loss if anyone could help.
thanks