It does nothing...The ECM doesn't even reference it...Our cars use MAF's for fueling purposes...The MAP's were referenced by the ECM on speed density setups...
But you pretty much got it, it only signals the boost gauge on the dash for analog dash cars...The digital dash cars used a different style of pressure switch to trigger the red and yellow boost lights on the dash...If your vacuum hose to the MAP is broken, then either plug it or replace the line...You will have a vacuum/boost leak at that point and will probably make your motor idle and run rough until you get into boost...It will cause your ECM to richen the mixture because the o2 sensor is seeing more oxygen in the exhaust because of the unmetered air being drawn in through the broken line...
