Slight throttle acceleration. Stumbles falls on its face. Almost acts as cyl mis fire. But my live data shows all ok. In park depressing pedal no hesitation or stumbles. What I did notice intake air temp sensor or air charge sensor reads -17 degree. Truck runs strong when pushing pedal off idle to 1/4 pedal and beyond. New IAC valve. Cleaned throttle plate. Clean MAF all actual values for these sensors With in factory specs.
thanks. Hopefully it’s this sensor.

 

You're saying there's an air temperature sensor telling the ECU that it's minus 17 degrees?
That could be your problem right there.

Did you buy a Motorcraft or Hitachi brand IAC?
They're the only ones which will work well as the signal the ECU puts out doesn't jibe other brands.

How many miles on this 1999?
A 20 oz. bottle of Techron before a stint of local driving might work wonders.
Call it "Crossing the T's and dotting the I's".

 

You don’t know if it’s the air charge sensor. Even though -17. Could have be other issues. These are all high mileage trucks we have a fleet at work frkm 1998-2013 or 14 is the newest. We have 140 ford rangers.
all our parts are from Napa or Fomoco. I just stated that sensor reading was out of place. It’s not gasoline
it’s fine trucks get filled up daily. Techton is not going to solve my issue.