First, clean the throttle body, they gum up with deposits from the crankcase breather. If that doesn't fix it, have the idle stepper-motor checked, they sometimes seize and won't allow the computer to adjust the idle. A new one costs around $65. The engine should be able to maintain 750 rpm /- 25. There was a TSB on earlier 2.5s (possibly 92 or 93) where we installed a jumper across 2 wires in the A/C connector to trick the PCM into thinking that the A/C was on, this gave an idle of 850rpm and smoothed things out some. The TSB gives a part# for a special jumper/plug to replace the protective cover on the A/C prep connector. The connector is a black six wire oval plug, above the firewall junction block, near the support rod to firewall bracket. Remove the protective cap, (you probably don't have A/C) and you will see 5 terminals in there. There are 2 blue/light blue wires diagonally across from each other in the connector, a small wire jumpered across them will tell the PCM that the A/C is on, boosting the idle rpm goal. The jumper needn't be much larger than a staple. Replace the cap and you're done. Hope this helps, good luck!
