Car accels to 70 mph, runs good for a few miles then starts to miss, decel down to 50 mph or so. Pressing the accelator down will cause car to downshift and engine revs to 3500 rpm or so and accels back to 65 mph. This cycle is repeated every few miles. Idle and low speed is smooth. 140,000 total miles or so. Only unscheduled maintence was timing belt about 15,000 miles back, it didn't break, was a belt tensioner problem. I have purchased a Code Reader (this car is an OBD I version), but I believe the Code Reader is defective, so I am back to supplier for a new one. I suspect O2 sensor and possibley MAF. Does anyone have any ideas? Thanks.
Bruce

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1997 RANGER XLT
EXT CAB
4.0 V6 automatic 5 speed tranny
16 inch alloy rims (first mod)
added 2001 factory radio from areostar van. single disc and tape deck.

have you checked the plugs, wires, and air filter? its just a thought...

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just my opinion.....

1998 ranger extended cab, 2wd, 4.0 ohv, 5 speed, sony xploid 52 4 way watt radio, 2 pair of pioneer 240 watt speakers, air horn, Cobra 29 LX LCD CB radio pushing 100 watts, k&n air filter, 15 inch exploder wheels, dual exhaust with 4 inch stainless tips, 2 10 inch subs with a 300 watt amp just for the hell of it!