I also have a 97 with the 4.0 and about 148k...Im tellin u right now it could be a number of things...Vacuum Leak, The Idle Air Control valve, intake gaskets, fuel filter, carbon buildup...Dirty Mass Airflow Sensor....Most likely the IAC valve is faulty or plugged up with carbon....Take it off and clean it out with carb cleaner...make sure to move the plunger up and down and then give it a coat of WD-40 inside...Try that first and let us know if that helps....If not, u should clean the MAF Sensor with Electronics cleaner....well u should do that anyways at least once every 6 months to a year...
