Drivetrain New hanging idle problem

7991LXnSHO

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On a 91 5.0 LX 5 speed, the idle speed has periodically staying up near 2000 rpm after The car has stopped. And it will stay with the high RPM idle each time I stop, until I turn the car off and restart it. Then it runs fine, with the idle staying up when the car is coasting, and dropping down when stopped.

I get 11 and 11 for codes. So I was wondering if the VSS or wires are acting up and sending that the car is still in motion. (I have a new VSS from Rock Auto on hand.) Then I saw Mustang5l5 post about the neutral gear switch in another post.

“The sensor on top of the T5 is the neutral Gear Switch. It’s job is to tell the ECU when the trans is in neutral (in parallel with the clutch switch) and adjusts idle strategy accordingly. Without it, you sometimes get a hanging idle. It has nothing to do with the starter circuit.

older t5s do not have it. The boss is not drilled. You’d need to find an 85+ top cover to retrofit it. Without it, you should jumper the plug on the clutch switch if you get a hanging idle.”

Did I buy the wrong part? And what’s a good way to test whichever part is most likely?

@Mustang5L5 @jrichker and anyone who has fixed a possessed car.
 
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Mustang5L5

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It’s wired in parallel with the clutch switch. If the switch is plugged in, press the clutch in. Is there a change in idle? It should drop. If not, it’s likely not the NGS.

also, you will get codes for these. Code 67 forthe NGS if you run the codes with the trans in nuetral and clutch not pressed in and the NGS is failed, and A code for the vss
 

7991LXnSHO

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Only codes 11.
The clutch makes no difference in engine speed when it decides to do this.
I am open to suggestions on what else to try.

Intermittent issues are annoying. Restarting the car is not always practical, but has “reset” something and made the car act normal for the rest of the trip or errand each time so far.
 

7991LXnSHO

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Now you mention it, I need to verify the switch is actually plugged in and making good contact. Anything else I need to check while under there? The list already includes measuring the sway bars and putting in rack limiting clips for other reasons.

On the top side, the throttle cable is not sticking and the IAC is not whistling the throttle body when this is going on. Except for this goofy deal, and being a bit cold blooded at start up on cool days or after sitting a couple of weeks, it almost runs like stock.

It is like an older horse that thinks it’s time to head back to the barn. It suddenly has a lot of energy and needs the reins held tightly. :)
 
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nickyb

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I've daily driven my 93 of for over thirteen years (30 miles round trip) and only once I had a hanging idle.It happened when exiting the freeway at the light.It wound up being the ect sensor.easy fix,and inexpensive part.
 

7991LXnSHO

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I have one of those on hand. I have not tested the ECT at different temps as per J’s specs, but comparing the new and original ones would be easy enough, and it might help the cold bloodedness if it’s swapped.

Any other ideas? I am open to suggestions beyond calling a priest for an exorcism.
 

nickyb

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I have one of those on hand. I have not tested the ECT at different temps as per J’s specs, but comparing the new and original ones would be easy enough, and it might help the cold bloodedness if it’s swapped.

Any other ideas? I am open to suggestions beyond calling a priest for an exorcism.
Did you fix it ?
 

7991LXnSHO

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It is supposed to snow for a couple of days, so it’s parked inside. I am hoping for another answer or test by the time the weather gets nice for the weekend.
 

breth3

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It is supposed to snow for a couple of days, so it’s parked inside. I am hoping for another answer or test by the time the weather gets nice for the weekend.
Hey Guys, I am having a similar issue. Did the ECT sensor swap fix it? I have a brand new Motorcraft IAC on my car and relatively new TPS.
 

7991LXnSHO

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Thanks, will try and I might as well check out how smooth the sweep is on a meter while there.
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@breth3

The Idle that hangs high and goes away when you restart the car is usually a TPS problem. Most of the time it does not set a TPS code 23 or 53. Try cleaning the TPS sensor contacts as a first step.
 

nickyb

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Hey Guys, I am having a similar issue. Did the ECT sensor swap fix it? I have a brand new Motorcraft IAC on my car and relatively new TPS.
it did fix mine,and is super easy to swap out.
 

Mustang5L5

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Hey Guys, I am having a similar issue. Did the ECT sensor swap fix it? I have a brand new Motorcraft IAC on my car and relatively new TPS.

did you dump the codes? Usually the culprit will show in the form of a displayed code that will point to the cause.
 
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