[P-hack]

Actually, for this, I'm going to say the "right" way is to use a single $1.50 microcontroller (i.e. attiny something), if your map sensor already has a 5v power supply you can set it up to run on an internal oscillator and have ZERO other components/chips (maybe a small capacitor or two). In the main loop you read the map voltage on one of the analog pins and use a pwm for the output to the meter that you constantly adjust (using a tiny program to map the input reading to the pwm setting).

If you are new to microcontrollers you can get an arduino uno clone for like $10 on ebay which makes it about as easy as it gets to get started, both in physically uploading the program to the microcontroller and in setting up your program. You can do this project with just an arduino and a computer to program it with too, just costs a bit more than a bare microcontroller.