ok so it all started with the truck making this howling noise comming from the intake, I did research and heres what Ive done so far:

Replaced IAC valve
Cleaned Throttle body
Cleaned MAF sensor

the truck runs good but my MPG sucks and when I go to stop the RPMs stay at around 1500 so downshifting is rough and then it wont idle down until the very second the wheels stop turning so it turns into a very hard stop.

If anyone has any idea what this could be please advise....

My other guess is the TPS but what do I know right? Im gonna end up taking the IAC back since there was no change after replacing it....

 

Major vacuum leak! check for lost and cracked hoses first.

 

I agree with bluewind ! The source of the howl is the source of the vacuum leak .

 

Of course you're all right; if memory serves correctly, the engines of this era used no name recyled condoms to make the intake rubber fittings. On these engines (both the 4.0 sohc and the venerable old 4.6L), they had rather large rubber 90 degree elbows for the PCV line. That's always the first place to look. On the 4.0, it might be between the intake plenumn and the firewall (bit of a tight fit, but not bad) at the LR of the intake in the back of the engine, but it's easily visable.
It also explains all the symptoms you stated, minus the CEL that's probably been on a while, but i could be wrong if it's just one of these things that just started.

 

Some guys just have a way with words. Wish I could do that !

 

thanks for the reply fellas. I also think it is a vacuum leak but
there is no check engine light on.
im gonna work on it again today and see if I have any luck.

 

here is the update:

I put the old IAC back on the explorer since there was no fix with the new one and the weirdest thing happend..... the high idle went away, the hard stops went away and the howling went away...... the only thing thats happening now is slight low idle at start up but now the gear shifting are smoothe and the truck is running somewhat better.

Here is my guess: The IAC IS bad but maybe the new one needs to be calibrated? or someone mentioned to me that the computer need to be FLASHED with the factory setpoints? I feel like im so close to fixing this problem.

What do you guys think about this one?



I checked for vacuum leaks and there were none.

 

I think you probably got the wrong IAC valve. They almost all looked alike, but the passages (or air holes in the valve) are prettey closely calibrated to a specific size for the particular engine displacement you're looking for (i..e, the 4.0L and 4.6L look the same, but the 4.6 will let a bit more air through, which creates a higher then normal idle).
There is a trick to these to help set them up. I'll write more later, when I'm not supposed to be working.

 

thanks I will look into that, I mean i did ask for the make and model I have... but what you say makes sence. thanks

 

I have a very similar problem with my 2001 Expl. In regards with a howling and the hard stops. If I go hard on the accelerator it just howls but does not accelerate, and after a cerain point the throttle seems to stick and stay at around 1200, so it is a hard downshifting. Even when I go easy on the accelerator, once it warms, I get the same results. That's why I am suspecting the gasess are not exhausting and pressure is building up in the engine. So that's why I suspect the catalytic converter being clogged. The DPFE exploded, so that was replaced, with high temp. hoses, along with EGR valve, and I get the same results. I checked the two hoses running to the PCV, and they seem fine. They aren't as stiff as new, but I didn't notice any leaks. PCV rattles, so I'm assumiming it's working properly. What else can you recommend I do. When I first got it in October it would pick up enough like normal, and I would take the freeway. And then all of a sudden, it just lost all it's umpf. And now I'm limited to the access roads for only so long, because once the throttle sticks, it will overheat.