it sounds like an electrical problem, since your alarm is messing up also. i would check to make sure that your battery is still within spec, along with your alternator. it may be that your alternator is starting to die, so it only puts out enough electricity when its spinning faster than idle, as is the case when you are driving. it could be a vacuum leak, but i would expect a throbbing idle, rather than almost no idle at all. i would also look at your ignition system, if everything else turns out fine, by starting with the ignition coil, then moving on from there.