Hesitation/Stumble at low throttle won't go away!

[Brandon96]

I've got a stumble or hesitation at low throttle and I'm at wits end trying to figure out why it's still going on.. I've replaced the whole motor and it won't go away!! :

The motor is basically brand new, less than 1k miles on all the hard parts and gaskets etc etc. Injectors are new. Throttle body was taken apart and cleaned. Both temperature sensors, the IAC, PCV, DPFE, EGR and both upstream O2's are new. Also worth mentions is my cam sensor, also new and aligned correctly... everything I can think of that would affect this has been replaced including the MAF. I may be leaving some things out so be sure to make some suggestions!!

Now, on to the MAF and my main problem. I can unplug the MAF and it will put the truck into the factory tune or whatever and the thing runs flawlessly. Hell I was getting 25mpg's highway! I first tried to clean the MAF, didn't work, I then replaced it with a junkyard sensor, still to no avail.. I've got a rebuilt unit in it now and the darn thing is still stuttering.

I am open to any and all suggestion to what this problem may be. My truck did this before and after the motor build.

 

[andre 244]

?
intake boot . did you replace the two intake gasket and upper plentium .coil pack
also check for loose plug
had that hapend to me replacimg 96 ranger ohc was loose plug
you can also try the wiggle the wirering when at idlel
thinking engine move some bad conection hope this help

 

[MR SCARY]

I just went through chasing a stutter problem.I changed complete ignition (coils,wires plugs,crank sensor,cam sensor,searched for vac leaks)Mine was the plug wires(problem was the same old wires or new wires).I have a 5.0 that has steel tube heat shields on the boots.I was shorting out to the heat shields.As soon as i took them off the problem went away.I'm not sure if you have the same on your 4.0 but just a thought.

 

[Brandon96]

?
intake boot . did you replace the two intake gasket and upper plentium .coil pack
also check for loose plug
had that hapend to me replacimg 96 ranger ohc was loose plug
you can also try the wiggle the wirering when at idlel
thinking engine move some bad conection hope this help

Yes, everything was replaced with the motor except for the coil pack.

The coil pack is just less than a year old, had it on both motors and it's in good working order. Plugs are new, 2nd set since the new motor and they're Autolites. Wires are new FRPP 8mm's.

As for the gaskets, everything's new and as far as I'm aware there is no vacuum leak. But it can't hurt to check again I suppose..

 

[Brandon96]

I just went through chasing a stutter problem.I changed complete ignition (coils,wires plugs,crank sensor,cam sensor,searched for vac leaks)Mine was the plug wires(problem was the same old wires or new wires).I have a 5.0 that has steel tube heat shields on the boots.I was shorting out to the heat shields.As soon as i took them off the problem went away.I'm not sure if you have the same on your 4.0 but just a thought.

The steel heat shields? I don't think the 4.0's are the same :/ Can you post a picture of what you're talking about though?

 

[Sloalty]

Is it only when you give it gas quickly? Mine feels like it stumbles then goes if I get in the throttle quickly. If I ease it on there is no stumble.

 

[lounge lizard]

I wonder if the "TPS" needs adjusting.

look for a thread on throttle positioning sensor for a write up on how to adjust.

 

[Brandon96]

^^

Nope, only under light throttle. For example when I'm pulling out of my driveway I have to give it just a tad of gas to pull up a hill and it stumbles and surges all the way up. Or when I'm cruising down the highway at 65mph, it's more like surging then but regardless it's only at low, or below 20% throttle.

Lizard I think you're on to something.. I know I adjusted it after I reassembled the throttle body after doing the "throttle body mod." But maybe it went out of whack when reassembly of the engine. Is it possible that the sensor is bad and sending random signals?

EDIT -- Answered my own question, THANKS GOOGLE! :;

http://www.buzzle.com/articles/symptoms-of-a-bad-throttle-position-sensor.html

The data provided by TPS is invaluable for proper startup, idle and easy throttle response of the car. These operations are affected when a bad throttle position sensor feeds erroneous data to the car's computer because of which the

Maybe I'll just try replacing it...