1995 Ford Bronco High Idle

Hello-
I have a '95 Bronco with fairly high mileage. Beginning yesterday when starting, the engine immediately revs up way above high idle. I asked and was told it was a leak in the intake manifold gasket. Does it sound like this is correct? I've never had any problems, but it runs at such a high rpm now, as soon as I let off the brake the truck just takes off and has no problem holding 30mph without holding the accelerator down! I've had all the fluids changed in the last 6 months and as said, it normally runs great.

Thanks!