1) Check all vacuum lines to make sure they're not cracked and in place where they should be.
2) Check the EGR system operation.
3) Check the vacuum switch on the front of the intake manifold near the thermostat - it has 2 vacuum hoses and often is cracked - even though it looks ok.
4) Check the rotor and distributor cap.
5) Check ignition timing.
6) Check the o2 sensor (it's about time to replace it).
7) Clean the ISC and throttle body.
8) Check the resistance values on the IAC, TPS and AFM.
9) Put in a bottle of fuel injector cleaner and as a last resort, send the injectors out for cleaning.
10)Another last resort would be to replace the fuel pump.

Frank