What sensors (or data input) could cause the throttle to stick or hang a bit at WOT?
Not pedal or throttle cable related and TB is super clean. It's a 97 4.0 OHV.
Here's what happened.. only twice, and I was not there the second time it occurred. With max AC on, pedal to floor going up hill, the throttle got "stuck" for a good 5-10 seconds. Thankfully at the top of the hill it unstuck and rpms came back to normal. The second time- same while max AC on, went to floor it to pass someone and got stuck on WOT- not sure for how long because the driver came to a (difficult!) stop and shut truck off not knowing what was happening. Everything was fine after that.
There was lots of maintenance and fixing of things within the last year, and truck runs really great more or less. I haven't tried to recreate this on purpose as it wouldn't be safe if throttle was to stick again. So i was curious if there was a setting or sensor or relay or basically anything electrical (or possibly vacuum/air related) that would tell the PCM to bypass or ignore or misread a setting related to closing of the throttle?

Things that come to mind to investigate-
TPS
MAF
IAC
Evap purge system
AC related?
Relays

Thanks for any input!

 

How many miles are on this '97 of yours?

When you select "MAX AC" the vacuum reservoir comes into play.
It's on the passenger's side of engine bay, bolted to the inner fender liner. Look down, beneath where the air filter housing meets its flex hose.
It assures there's enough engine vacuum to fully close the blend doors.

I believe shutting out all the warm air circuit AND closing a recirc door is involved but I am not certain.
Since you had MAX AC on, that hardware was involved.
This reservoir and its lines can be a vacuum leak source.
There have been numerous posts regarding breaks and disconnections of this hardware.

Have you looked at the accelerator cable with the engine OFF and the decorative cover (which says, 4.0 L SOHC) removed?
Try flooring the pedal then just to see if something is physically sticking.
Make sure all is clean. You can actuate the throttle body with the engine off and safe. Perhaps you can feel a binding or sticking.

Who knows....maybe any sticking is at the pedal end of the cable?

I can't imagine anything 'holding the throttle open' aside from the cable or internal binding.
Perhaps a broken return spring is involved?

Also, with help from a pal, run the engine with the brakes on hard. In Drive, see if the engine rocks a bunch when given some gas.
Bad engine/transmission mounts are often involved with run-on conditions.
BE CAREFUL WHEN YOU DO THIS.

 

She's got just under 166,000 miles which I'm proud to say 120,000+ are from me within the past 11 years. This truck is in pristine condition and was my daily driver until this past year- she doesn't like not being driven regularly! So now when I do drive it, seems new issues are starting to slowly arise.

I've checked out the throttle cable thoroughly, it's not stretched or binding/ sticking. Nothing catching the pedal, no broken hardware. And the whole intake & throttle body itself are super clean- butterfly doesn't stick. I've been thinking about this a lot. Things are hard to describe online, and I like to give too much detail just in case something that doesn't seem related might be helpful to know.

There's been a P1443 (purge valve /flow etc) code for a while that was cycling but finally remained on. The evap line was actually one of the first things I needed to replace when I got the truck, but it seems those hoses are rotted again. Would a vacuum leak in the EVAP line cause any issues like an air leak in the intake would?

No signs of an air leak, it would have to be really tiny if there is one- the majority of gaskets and hoses have been replaced within past couple of years. There is an ever so slight stumble in the idle currently. And I could try to describe how the idle acts on cold start until it smooths out, but would be better if someone else could actually observe it in real time..

The vacuum lines for the ac seem okay as well- I do have a blend door problem, but it's either a broken gear in the actuator or more likely the door itself is stuck (I haven't wanted to tear into it yet to find out since the MAX ac still bypasses engine bay). I can hear the vacuum pressure in the vents when changing the air off and on. How else can I verify some of these components to be sure?

I haven't been able to check the engine mounts officially, but I kinda doubt they are playing a part in this. Visually they look good. No idea about the transmission mounts tho..

Seems vacuum leaks are what I need to keep hunting for at this point.

 

Thinking more.. the evap line feeds into the throttle body. Even though intake air leaks and evap leaks are diagnosed differently and are different systems, either would still be considered a vacuum leak, yes?

I'm going to replace my evap purge lines regardless at this point, and I'm curious to see if that fixes some of the other "quirks" this truck has developed. Not sure when I'll get around to it (lack of free time) but I will update when I do, and if there are any changes - though I'm still not comfortable trying to recreate the WOT sticking issue, so might not be able to tell for a while if these are related.

 

"... intake air leaks and evap leaks are diagnosed differently and are different systems, either would still be considered a vacuum leak, yes?
Like the PCV system too. Any leak after the MAF is an intake/vacuum leak.

The EVAP system purge valve in my 2005 is in the engine compartment.
It opens to effect airflow through the all the hoses of said system plus the airspace above the fuel level in the tank.
If it's closed, any leak in the EVAP system would have to be between this valve and the intake manifold.
Again, in my 2005, the hose from the valve to intake is a molded hose 1 foot in length.
I don't know when the ECU decides to open this valve. It may or may not operate at WOT.

I'm uncertain of how the system tests itself.
With the valve closed, a vacuum could be affected, verified then waited out to see if there's a leak.

What the P1443 means AND DOESN'T mean is important to know.
Does it mean "a bad valve" or could it include a malfunctioning vacuum detection sensor in an otherwise working system?

Maybe a smoke test could reveal something?

 

I have replaced the evap purge hoses, solenoid and thermistor- I basically got the whole assembly for the one specialty molded hose that is a different size on each end.. the sensors I had were likely still good (I'll keep them in reserve) but I know the hoses were cracked. Anyway, went for a drive and the cel finally went off. I already knew this is what needed to be done, but was in no hurry for not having to pass emissions test here. But until recently, I had not considered that also being the source of a vacuum leak, silly me.

I'm still not going to try to recreate the throttle stick that happened on purpose, but I'll eventually be driving under the same conditions and see if it happens again. And if it does, I will come back with an update!

Still some other quirks that may or may not be related; I'll have to start new threads for those questions when I get to that point though..

 

I really don't think it's transmission related. But if it was, I would suspect something in the overdrive engaging- I can only assume this happened in the same gear on both occasions.

For me-
While being in overdrive, then when floored the pedal, it downshifted to passing gear and reached WOT and that's when it hung- where it should have shifted back up.. back into overdrive- which is still forth gear- unless it drops down to third? No idea which gear it got hung in. Hard to tell and many more days have passed since this happened! It's a 5 speed auto but it still technically only has 4 gears because how the overdrive works I think..? I can't remember now! This is why I miss driving a standard. You know exactly what gear you're in lol.

i don't remember if I have the 4R55E or 5R55E but they are the same internally.

I can say whenever I do randomly turn off overdrive, (mostly to make sure the button still works as well as overdrive functioning) that everything operates as it should.

How can I be sure to rule out this random issue being something in the transmission..hmmm..

 

For what it's worth to anyone reading this- the throttle has not gotten stuck again so far. The random "idle sputter" that was briefly mentioned in this post along with some of the "other quirks" were related to dirty spark plugs. I still need to fix what's causing the plugs to get fouled up so quickly as they were less than 3 years old with barely 10,000 miles on them (motorcraft double platinum).. valve related I'm guessing - maybe that's also whatever made the throttle stick, hmmmm..?? Or, the problem could be just being in Florida haha.