1991 Dodge Spirit 2.5 TBI (155K) bad idle slowly drops to 100 RPM then pops back up to 700 RPM as it warms up. Idles good in park (800 RPM). Idles fair in drive (700 RPM). Idles bad in drive with AC on (oscillates 700 RPM to 100 RPM 20 seconds cycles). Over two years replaced fuel pump, fuel filter, O2, MAP, PCV, Vacuum hoses, plastic T's. Verified and cleaned TB, TB fuel injector, TB pos sensor, and idle speed motor. Checked gas vapor purge hoses. Reseat wiring harness/connectors. Good air, trans, and oil filter. Was getting 23+/- MPG HW/city and it slowly dropped to 15 MPG (with heavy AC use). Gone up to 17 MPG (with AC) and better acceleration after new MAP. All the other fixes made things slightly better but not the idle. Runs good for a few minutes but after 5-10 minutes running good (with AC in drive) it starts to oscillate RPM on idle, acceleration starts to decrease and check gauge light comes on until RPM goes up to 800. Sometimes if I barely press and hold the gas pedal, RPM goes up to 800 and gauge light goes off but has less acceleration. Good charging system. No error codes. Highways are no problem. MAP vacuum line is open but slight restrictive. Upon further study, when at a stop and I crank the steering wheel it also drops in RPM and almost stalls. Added R-12 to AC a few years back and it still blows cold.