Good morning group,

I am writing today in hopes of getting pointed in the right direction. Background, I have a 1995 Bronco XLT with a 5.8L and E4OD. Since buying it, I have a high idle when it is warm, in neutral, and A/C off. I have checked, double checked, and triple checked for vacuum leaks, set the TPS correctly, swapped some sensors from another vehicle, pulled codes, switched PCMs, etc. Even changed the plenum and intake gaskets. I can 100% verify it is not cause by a vacuum leak or a bad sensor issue.

I have discovered it has something to do with the transmission. I will have the truck warm and its idling at 900rpm to 1000rpm. I unplug the MLPS connecter from the sensor and the idle drops to a proper 650-700rpm. Plug the connector back in, it idles back up. Ok, so I changed the sensor convinced it was the issue. Even with a new sensor, it acts the exact same way.

So my question is, can someone explain how those circuits work, and how to check proper function? I want to verify the correct wires have the correct voltages during the correct shifting points so I can see which circuit is causing the high idle. I tested the MLP sensor signal and get 5 volts with the key on. What I need to know is does the sensor signal return see 5 volts at some point during shifting that tells the computer to idle up when shifted into gear? I assume it is designed to increase idle when in gear to compensate for the addition engine load.

Thanks for any help.

 

Ford Chassis Master tech and passed the trans exam too
Never have seen any info regarding what you are asking in Ford books
Your 1995 MLP sensor has switch testing in the book but you mainly rely on PID monitoring with the Ford NGS
Note
When you disconnect a sensor (any sensor)
The processor uses data tables to extrapolate data and make the truck run
An increase in idle speed would be considered normal to me with just about any sensor disconnected
* I would be looking at a idle speed concern in the book, and see where that diagnosis took me
Basically, you would be checking the MAF and TP voltage and the fuel trims
You are disconnecting and working over the MLP is possibly futile

 

But the idle drops when I disconnect the MLP sensor.

What I assume is when the MLP senses a gear change, it will increase the idle to compensate for the increased engine load. What I think is happening is that the computer thinks it is in gear all of the time, so the idle is always increased.

I need to know what the computer is looking for to know when it is in neutral.

 

Drops or raises, but I am with you there
Still, I'd have a book out at this point going over an erratic idle concern flowchart and pinpoint testing for idle speed control
1995 PCED you want to read a bunch of it and find a NGS to get PIDS, do a cylinder balance test etc
Doing an engine running test with a Ford NGS scan tool is liable to come up with something on that 95
I have one of these, you need to borrow one

 

IMO
Your assumptions are correct
The processor uses your foot feed (TP voltage) VSS signal, (speedo) and brake on off to determine shift points and everything else
New Lincolns will be using the accelerometer sensor, steering wheel angle sensor and ABS brake info as well
All of that goes into the trans program and the drivability profile
That part keeps getting better and better, every year, within reason, albeit with some major problems along the way

 

I might have a 1994 PCED and can post some pages out of it in a few days if you are still having issues and cannot find a NGS with a willing owner near you
Most of us help people out for free for just a code test or some diagnosis
Ask AutoZone if they know any Ford techs that might have a NGS
They call me all the time, so does O reilly, not just for that of course

 

Easy button, Check for codes, even if light isnt on could have stored codes, most of us use this $30 OBDI code reader, takes the guess work out of counting flashes, best $30 ever spent, have you tried unplugging the IAC and see what happens.

 

I have one of these and use it all of the time. No codes are present on KOEO or KOER.

Unplugging the IAC lowers the rpm to 650.

 

Unplugging the IAC should drop the idle to base idle (around 550 rpm) and just about die
Can you watch your O2 sensors switch with that scan tool?
No is right
Watching them switch is a bonus to know what is actually happening
Most people have no idea of an O2 sensor switching
Are you one of them?
You need to be smart to fix cars these days
A O2 sensor stuck lean or rich, or switching like it should be, needs to be checked
You can do that with just a DVOM by backprobing the sensor
No need for a fancy 5k scan tool for that