Humming noise and MAP

For the engine speed fluctuations, when this is occurring, hold the accelerator pedal perfectly steady, then with your left foot, tap on the brake pedal very lightly, or hold it down steady about half an inch. If the engine speed stays higher and steady, the surging is being caused by the lock-up torque converter. The two most common things that will cause that are a mis-adjusted brake light switch, and on older cars with the common sense throttle cable, dirt in the throttle position sensor. Either one can send false signals that you will never feel, but the Engine Computer can interpret as one) you are planning on stopping soon, or two) you are planning on accelerating harder than normal speed variations while cruising. It unlocks the torque converter in response. That is similar to riding the clutch pedal on a car with a manual transmission. The torque converter will relock after one or two seconds when all the conditions are met. That is when you will see engine speed drop about 200 rpm's.

If no one else chimes in for the headlight adjustment, I will research that and try to find the solution.

The MAP sensor will be shown on the vacuum hose routing diagram under the hood. Be aware though that fault codes never say to replace parts or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a code, it is actually the cause of that code about half of the time. First you have to rule out wiring and connector problems, and mechanical issues related to that part.