I've got this 99 ranger with the 3.0 and she stumbles just a bit off idle. In fact the idle isn't exactly smooth but it's acceptable. It's when I step on the gas that she stumbles briefly and then comes on OK. This event happens in & out of gear. I've changed the plugs to the motorcraft fire wire, bosch performance wires.I took the truck to a friends shop and he hooked up an assortment of dianostic tool that basicly indicated that there wasn't a problem. (no codes) We cleaned the MAF TPS throdle body & I run about 3 oz. of lucas fuel injector cleaner in a tank a couple times a month.Oh yea , it;s more noticeable when warm but if I shut it off for a few( 10 to 15 min) & fire her back up she runs on all cylinders for a bit, then it,s back to the stumbling*** Any help will be appreciated

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She's just a black extented cab/ 4 door 3.0 w/ a 5 speed auto. Nothing really extraorniary but she's all mine.(& it's all one color w/ matching tires)