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A buddy of mine has a 1997 Ford F150 with the 4.2L V6 engine. After you drive it for a couple of minutes then stop at a stop-sign or red-light, the idle will “surge” — like it’s trying to stall out and then revs up to recover, over and over. Sometimes it will actually stall… And the fuel-mileage has become VERY poor since this started.
Scanned it with a scanner, no OBD-II codes, no freeze-frame data, no nothing. Ran a “live data” log while driving it for about 10 minutes… It *seemed* like the long-term fuel-trim was a bit high — but that was near the start of the drive, so maybe that was just while it was warming up? After a short while all the fuel-trims started shifting back and forth, just like you’d expect. And the O2 sensors were all shifting back-and-forth quickly, just like you’d expect a narrow-band O2 sensor to do. Engine coolant-temp, MAF-sensor, TPS-sensor — all the stuff I was monitoring looked completely normal to me… Yet it will continuously “surge” and nearly stall out every time you come to a stop. (If you put it in Park, the surge disappears, btw.)
So, what could possibly be causing this? I have no idea where to even begin with no OBD-II codes.
Thanks for any help you can give,
Laurence MacNeill
Mableton, Georgia, USA
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