Thank you to all who replied. I just picked up the car from the shop. Here's what they found.
They read the car's on-board computer and found two trouble codes. One was for the idle air control valve (apparently not the same thing as the MAF). It was clogged with carbon deposits.
The other code was for the crank angle sensor. This sensor apparently tells the spark plugs when to fire, depending on the position of the crank shaft.
They replaced the crank angle sensor and cleaned the idle air control valve. The car is running great once again. 200,000 miles, here I come!