That's a pretty good indication of a wiring problem or possibly a failing MAP sensor. 33" implies positive pressure on the MAP sensor vs the standard vacuum. Highly improbable without backfiring or broken intake valve. A plugged restrictor can't create pressures at the sensor that are above ambient pressures at seal level.
The MAP sensor is really a transducer that sends a variable voltage based upon the pressure/vacuum it is seeing. At 30" (it's max reading), it sends 4.7 volts. So, if you have a wiring issue of failing transducer that is putting 12 volts (the voltage provided on the power feed of the transducer) on the return wire, you will go to the max reading, as defined by your instrument. I would expect most EMS provides to have a max of 32 or 33" on this reading.
Larry