It may mean all you have is a clog in the port on the rear of the
TBI where the vacuum line goes to the MAP sensor. Even a tiny
bit of carbon or dirt will not allow the proper amount of vacuum
sent to the MAP. Clean out the port using carb cleaner and I've
used pipe cleaners to get junk out. Also check the vacuum line
itself for any tiny splits or cracks. One way to test it is plug one
end and blow a small amount of air into the other end while
emerged in a bowl of water. If bubbles show up, then you know
there is a prob with the vacuum line. Again check for vacuum
leaks with the motor running and spraying soapy water around
the base of the TBI and other vacuum port areas.
A split in the MAP vacuum line from the TBI to the MAP may or
may not show up as high vacuum sig. MAP's are not
that cheap, so simple tests might save you some money.
However sometimes the MAP itself can go bad via a bad
Here's an idea of what they run.
Here is a really good article on MAPS.