Do you have a multimeter (you know, to read voltage and resistance) and stuff? It's check for the 5V on the MAP sensor. It's probably plugged in right next to or on the throttle body. (I'm not sure because i have an STI.) I'm not sure exactly what the Atmospheric Pressure Sensor uses for voltage readout, but it should be pretty close to 5V, depending of course on what the pressure is where you live.
Check the input voltage first, and then the output. If the input is good, and the output is bad, it's gotta be the sensor. If the input is bad, well you know, it's something further up the line.
When troubleshooting electrical problems with any type of test equipment, in this case a multi/volt meter, always "half split" the circuit. Example: check half way in the circuit, and then check again in the direction of the bad reading. Its the easiest and most accurate method.
P.S. if you don't have a multimeter, you can buy one at any auto parts store or radio shack type place. They are anywhere from $20-$300, and yes, the $25 ones are just fine if you don't need all the bells and whistles.
Let us know what you found out.