Engine Performance problem
2001 Ford Windstar 6 cyl Front Wheel Drive Automatic 195000 miles
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While traveling at a constant speed on a flat road the engine begins to shutter or jump. The engine does not do this while at an idle or while coasting or while the van is accelerating or going up a hill. I have used the actron obdII pocket scan code reader to try and discover the problem but after a complete diagnostic it says there are not any faults or trouble codes and the mil is not on or has ever came on. The only warning light that ever comes on is the abs light and the brake warning light they only come on periodically and never at any type of regular or predicable times. all fluids are topped off. i have some ideas as to what might be the problem but i really need an experts opinion before i waste time and money trying to do the dyi thing. please help

this shudder is your torgue converter lockup mechanism. I think maybe the switch might be going bad, take it to a transmission shop and just explain whats happening and they can tell you if thats it. I'm almost 100 percent positive, by what your telling me. I think there is a way you can unlplug the switch just to see if it still does it and if it doesnt then thats how you know its definitley the switch.