You can buy a 4.7 Volt ZENER diode, put in in-line with the MAP sensor. This fools the computer by sending a MAX of 4.7 volts to the computer. This voltage is just low enough the computer doesn't see it as over-boost.
I got my ZENER diode locally from a TV repair place. They ripped me off -- charging $7.00 for ONE. You may be able to find one for about $2.00 (another place a few hours away from me has them this cheap)
Good luck.