1996 Ford Contour - engine just revs on start

In particular, the tube that comes off the brake booster and drops down between the firewall and motor are somewhat common to crack and allow excessive air into the motor. The ecm see the air and commands more fuel, thus the racing idle. No promises! :)

Based on the updated info, I would access the throttle plate and check it for a carbon build up. I'm more inclined to think the plate is getting wedged open (not good if you're driving). Castle makes a good cleaner for that, I usually use a bottle washer type of bush to scrub it out at the same time. This may throw the check engine light on from the cleaner temporarily.

The cracked tube isn't easy to spot wothout using a smoke machine, but not say it's impossible or that you have this or the above. :) Good luck.