Your car either has an electronic or mechanical throttle. Electronic meaning theres a sensor that tells the throttle where is should be, mechanical meaning there's actually a cable that goes from the pedal to the throttle. I would need to know which to accurately help. If it's electronic, make sure the pedal returns all the way to where it should be (pull it up slightly with your foot or hand while the car is off, if it comes up get it checked out, if not you have a glitch in the computer somewhere or a bad sensor). It it's a mechanical link, make sure the throttle (it will be near your intake manifold) moves smoothly and returns to where it's supposed to be... You could also have a vacuum leak somewhere, so check all the hoses coming off the intake manifold and such to make sure they're connected and not split. Sometimes you can't see a small hole in one of the hoses, just an F.Y.I.
As for the leaking coolant, check your radiator and hoses to make sure they're not leaking. If they're fine, then the leak is coming from either the heater core or the block/heads, which is pretty costly. Is your exhaust invisible after the car is warmed up?