I have a 93 Integra and when the key is in the ON position, but engine not running, there is a buzzing noise coming from behind the driver side headlight.

Anyone know what it is?

Also, when I come to stoplights and stop signs, my idle sometimes drops a little lower like the car is going to stall. The car has a new tune up (plugs, cap, rotor, timing belt, timing adjusted, PCV valve, air filter). It will just go up and down from about 800 RPM to 200 RPM.

Any ideas?