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I’ve got a strange question for the tranny guru, is it Mark?
Vehicle is a 2000 Expedition with 4.6L and 200+k miles.
Its my son’s vehicle and he is chasing an intermittent hanging idle.
Once in a great while, when he slows down to Come to a stop, the throttle feels like it hangs at like 1200-1300 rpm, and it feels to him like the torque converter clutch is still locked up and it feels like a standard shift where you forgot to push the clutch in.
So we have discussed this (he lives 150 miles away) and we are wondering if the hanging throttle is causing the torque converter clutch not to release, or if the torque converter clutch not releasing makes it feel like the throttle is hanging.
So the question is, what is the logic and what sensors are involved in locking and unlocking the torque converter clutch?
The converter clutch staying on does feel like the throttle is hanging. I don't think your throttle is hanging. Fixing the converter clutch problem will almost certainly fix the hanging throttle issue.
The most common reason for this to happen is low trans fluid. With the transmission warmed up by driving at least 10 miles, check the level with the engine idling and the trans in park. If it needs fluid use MERCON V.
The next step is to read the codes. Even if no lights are on or flashing there could be relevant codes stored. Forscan is an excellent way to read the codes. You can download it free at Forscan.org. You will also need an ELM327 adapter. I bought one from Amazon for less than $30. The places that read codes free CANNOT read these codes. If you don't get Forscan you'll need a good independent shop or a Ford dealer.
Thanks for the reply. I think we can eliminate the TCC as the cause.
Throttle hung as he was coming to a stop so he bumped it up to neutral and the RPMs climbed another 200 RPwM.
So I think the TCC is good.
Since the fuel trims are reasonable, I don’t think it is an external vacuum leak.
I’m thinking it’s an “internal” leak.
Maybe the PCV valve is not closing.
Or the IAC pintle is sticking.
Or maybe the EVAP purge valve is bleeding air/fumes into the intake.
He’s pretty good with AutoEnginuity and has data logged and graphed (see below) desired rpm vs the actual rpm as well as the TPS voltage and the IAC duty cycle. Additionally, when the TPS voltage equals the TP RATCH PID the TP MODE PID shows C/T, indicating the PCM is recognizing the closed throttle position. Just gotta be logging the data some time when the throttle hangs.
Thanks again for your reply Mark.
Just to wrap up this tranny thread, under what conditions does the PCM? Decide to unlock the Torque Converter Clutch as the vehicle slows down?
It will unlock the converter when the accel pedal returns to the idle position. It will also unlock below a certain vehicle speed no matter where the pedal is.
Thank You , Mark.
That’s “good to know” info.
I’ll have him add the TP MODE PID to the data he is logging.
When it shows “C/T” the TCC should be unlocked.
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