Cause of High Idle?

[LorenS]

Friday I serviced the transmission, including taking out the valve body to replace plastic accumulator piston with metal one, (manual valve?) to allow flow to torque converter while in Park.  I have noticed the last couple of days that the truck - even when warm after 30 mile drive - idles higher than normal, around 1250 versus 800ish RPM.  This is in park or neutral.  The tach isn't wonky, I only looked at the tach because it sounded fast.  Idle while in drive seems normal.  I have checked the transmission fluid after 30 mile drive home on interstate, truck in neutral on level ground and it's in the middle of the hatch mark, same as the last 30k miles.  Fluid is not "foamy".

Anyone have any ideas on what may cause this?  No other symptoms or driveability issues.  Fuel pressure same as always, engine temp the same, EGTs run the same, voltmeter reads the same, even the MPG estimator seems normal.  I'm befuddled!  Had over 200 miles on the tank of fuel before symptoms showed up.

[Timd32]

Could your TV cable somehow be causing issues with your throttle linkage? Maybe something is hung up there, if the TV is not set correctly you will have some other issues for sure in general. Just looking for common areas between the throttle and trans.

 

 

[Mopar1973Man]

I would check throttle linkage when it idling high. See if the APPS is fully resting on the stop pin.

 

Did you attempt to adjust the APPS voltage? If so this can happen need to drop 0.1 to 0.2 below the tag voltage. 

 

Bad APPS sensor possibly...

[LorenS]

I have not adjusted anything near the APPS, which is a Timbo, but I'll look to see if it's at the stop. I'll also look at the TV cable and return spring under the truck.

Thanks, gentlemen.

[Dieselfuture]

Do you have quad, possibly something in settings if you do

[Me78569]

read live data from your IAT and ECT sensors.  are they accurate?  If the IAT got damaged and read low temps it would cause high idle.

[LorenS]

 

1 hour ago, Dieselfuture said:

Do you have quad

No tuner of any kind, though I do desire to purchase one!

 

Meant to unhook batteries when I got to work but forgot.  Hoping a little battery-free reset will do some good.

A fellow here also recommended I check to make sure the MAP sensor is reading correctly, that "if he recalled correctly" the MAP sensor reading can trump the ECM's desire to idle at 850ish.  Will read the OBDLink with engine off before unhooking batteries to make sure it reads 0 PSIG, ~14 PSIA, or equivalent in metric.  As a side note, the air filter is newish and still very clean.

 

Is it possible that I have a lot of oil blowby though the turbo causing such a problem?  I have strong doubts that's the problem because the truck drives the same as always and the idle is super stable.  This issue also came up IMMEDIATELY after transmission service.

 

The 8-way electrical connector went back together exactly as one would expect, smooth with a nice click.  Could I have done something wrong in the valve body work to cause this?  Pressure/temperature sensor connection wasn't removed, and I did push on it just to make sure it was still connected before putting it all back together.

 

While crawling under the truck, I noticed my red CAD vacuum line worked its way out of the elbow (again).  I reconnected that while the engine was running, and to absolutely no surprise at all nothing happened with the idle.

[Mopar1973Man]

Actually a bad ECT sensor reading low will cause high idle. IAT sensor does noting but jack up timing more hence the high idle switch, but if the software is enabled it should cancel after 170°F the resume normal idle at 800 RPM.

[LorenS]

27 minutes ago, Mopar1973Man said:

a bad ECT sensor reading low will cause high idle

The ECT is used by ECM which then feeds a signal to the dashboard gauge, correct?  Or are they a parallel circuit with the gauge and the ECM reading the same sensor but not affecting one another?  I ask because the gauge reads the way it always does, but if it's a parallel path then the wire feeding the ECM could have an issue and make it up the idle, right?  The fact it all started with the transmission service is the odd thing to me.  The "high trans temp" light isn't on, but does the engine high idle to circulate fluid when it believes the transmission is hot but not "so hot I need to light the dummy light"?

 

It's not cold enough to warrant it, but last night I plugged the truck block heater into the timer, so when I fired it up this morning the engine idled at 850ish (did not think to look at ECT on OBDLink).  Got to work 25 miles later and the engine idle was up.

 

I did not add a drain (nor a temp sender hole) to my transmission pan, so sure hope I don't have to drain it to wiggle the temp sender wire!  Is there another temp sensor wire I may have bonked/tweaked/jostled on the outside of the transmission case?

[LorenS]

"Absolute Throttle Position" is now showing 4.3% even with my foot off the pedal and throttle against the set screw under the hood.  I still have not unhooked my batteries for a reset of sorts.  I haven't touched the APPS in thousands of miles; bought a TIMBO from Mike months ago, and when I went to put it on found out that's what's already installed! So, I have a spare TIMBO.

 

ECT and IAT all seem correct.  The MAP sensor registered 14.8 PSIA even with the engine off - that doesn't normally make sense in Kansas City, but NOAA confirms we're at 30.3 inches of Mercury today, aka 14.8 PSIA!  Bright blue skies today.

Do I follow the "Stopping the Myths" directions to make sure I'm below the voltage?  I have not touched the set screw under the throttle cover.  

 

[Me78569]

4.3 % at idle state is your issue.

[LorenS]

2 minutes ago, Me78569 said:

4.3 % at idle state is your issue.

That's what my first thought was, but wanted to make sure it was as straightforward as a bell-crank set screw adjustment, and not a "false" 4.3% reading based on who-knows-what designed in the PCM or body computer, because of a Daimler-Chrysler summer intern designed Rube Goldberg way of doing things.

[LorenS]

"Fixed" the problem with the adjustment screw, but still can't determine what caused the need to adjust it a whole turn or more.

[Mopar1973Man]

APPS sensor most likely wearing out.

[LorenS]

I've had to adjust the screw at least 6 times so far, sometimes after driving only 22 miles or so after driving to work!  It's not surprising, I suppose, it seems very loose.  Any recommendations on something to 'gum up the works' a little?  LocTite Blue seems a little extreme, but I don't want anything very tacky, either, to get covered in dirt and grime and cause other problems.

 

The screw is working its way in, raising my idle speed.  As many times as I've turned that screw "out", it'd be all the way out if it wasn't going back it on its own.

 

[Haggar]

I can't picture the screw you are talking about, but one possibility can you replace it with a longer screw and use a jam nut to help hold it?  another option is to "disturb" the threads a bit.  Use a soft hammer to make the male threads deform just a bit.  Loctite  makes a purple thread locker.  I use it for smaller screws (like scope mounts etc)  it seems to be good to resist light vibration and it is easily disassembled.

 

HTH

Hag

[LorenS]

Thanks, Haggar
I'll definitely look into the purple Loctite.  I also like the idea of the longer screw and a jam nut.  I don't really want to mess up the threads in there!