I'd check the following:
1. Change your air filter.
2. Check & test Fuel Pressure Regulator.
3. Check your other vacuum devices for proper operation and verify the hoses are in good shape (not hardened, cracking, or tearing). This can be done with a vacuum pump if you have one or can borrow one. ($25 a cheap parts store, Meijer, or Walmart)
4. Check & test Idle Air Control Valve.
5. Clean airway passages for IAC and throttle body.
6. Oxygen Sensor. (replace if you don't know how old it is)
7. Test Air Mass Meter for bad values is the previous steps haven't solved the problem.

A note on the O2 sensor, you can have a dying O2 sensor and still get valid readings out of it. This is deceptive and confusing since the sensor still shows voltage, but tells the computer to correct for a 'false' lean condition. The computer enrichens the mixture, the O2 sensor is happy, and the car thinks that it's ok. (except that you're consuming a lot of gas and your gas milage has dropped 2-5 mpg or more).

Art Bernstien had this problem and you can read the details in the following post:
http://www.brickboard.com/RWD/index.htm?id=618018

Good luck and God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 214K