The 1990 2.9l used a MAP sensor as the main control for Fuel/Air mix, it was called a Speed Density system.
MAF sensors were used in later years, Mass Air Flow systems, the MAF system was more accommodating to engine wear and changes over time.
Many racing engines are setup to use MAP systems as these are better suited for fuel injection control in non-standard operation.
MAP sensor would be on the passenger side firewall, some times hard to find behind wiring, it is small square usually black plastic, it will have a vacuum hose connected(best way to find it) and a 3 wire connector.
These can't be cleaned, but vacuum hose often leaks which causes fuel/air mix issues, from high or surging idle to bogging and stalling.
If you put good vacuum line on MAP then suck on it, it should hold a vacuum, if not replace MAP.
MAP sensors rarely fail, not never, it just shouldn't be replace without looking at other possible causes of engine problems.
Last edited by RonD; 04-06-2014 at 11:59 AM.