2003 t444e idle acceleration

Desertsparky · 01-16-2023, 02:35 PM

Our 2003 t444e/allison 2000 when idling will start to accelerate after some time. Just a quick press of the throttle will stop it. Seems to happen after idling every few minutes. Any ideas of causes or fixes. It doesnt seem to go to an unsafe level but it concerning especially if I leave the wife and or kids while I run in to get my change etc.

rossvtaylor · 01-16-2023, 06:24 PM

Do you have an air throttle system? If so, the treadle valve might be leaking which would create the symptoms you're seeing.

cadillackid · 01-17-2023, 06:45 AM

if the weather is chilly this is called CAP.. and its turned on standard on all T444E's..
it is called Cold Ambient Protection.. after 5 minutes at low idle the bus will idle itself up to a maximum of 1450 RPM.. and attempt to reach a coolant temp of 170.. when it starts to get close the idle speed will automatically come back down.. I think this activates anytime the intake air temp sensor reads 45-50f or below.. id have to read the manual on it again to be 100% sure...

all you have to do is touch the accelerator or brake pedal in less than 5 minuite intervals and it will reset that timer

you can typically tell when the system is armed.. as when the bus starts up in semi-cold mode it will udle up to 900 RPM until coolant temperatures reach osmeplace around 85-90 then it comes back to the normal 700 (unless CAP activates)...

in REALLY COLD weather, the engine will idle at 450 RPM until the Lube oil PSI reaches 20-30 PSI then it will slowly come up to 900.. (and higher if CAP activates)...

im not sure if these features exist on the DT466E or not.. you can turn them off in the ECM if you dont like them..

cadillackid · 01-17-2023, 06:47 AM

I should add that if you park a Warm already-driven bus and idle it.. the coolant temp will drop from heat being removed by the heaters.. and CAP will acticvate as the coolant temp drops further from 170... its not just a startup thing..

rossvtaylor · 01-17-2023, 11:37 AM

Damn, Christopher, that makes sense. And it's clear that I don't know much about these newfangled computerized engines. I think of things in terms of mechanical causes and didn't know about this.

So, Sparky, forget what I said. And thanks, Christopher.

cadillackid · 01-17-2023, 01:11 PM

Quote:

Originally Posted by rossvtaylor

Damn, Christopher, that makes sense. And it's clear that I don't know much about these newfangled computerized engines. I think of things in terms of mechanical causes and didn't know about this.

So, Sparky, forget what I said. And thanks, Christopher.

the only reason I know is because the first time mine started speeding up I of course (coming from working on old mechanical diesels) thought it was getting ready to run away and blow up!!!

till I ran into the cab pulling the hood latches on the way.. and turned the key off (just to stop any fuel).. and to my surpise the engine just shut off like normal....

so I got the books out and started reading... and found the option in my computer where it exists and it was (is) turned on..

Desertsparky · 01-21-2023, 08:49 PM

Sorry it took me so long to get back to you all. I want to say it did it in summer as well (in phoenix). I know its not a mechanical throttle. Ill have to look at it closer in the morning. I assumed it was electronic but I'll check for air lines I'm guessing?

cadillackid · 01-22-2023, 03:34 AM

Quote:

Originally Posted by Desertsparky

Sorry it took me so long to get back to you all. I want to say it did it in summer as well (in phoenix). I know its not a mechanical throttle. Ill have to look at it closer in the morning. I assumed it was electronic but I'll check for air lines I'm guessing?

if its truly a pedal problem or issue with the TPS and not the CAP system then tapping the brake pedal would have no effect.. the CAP is disabled by tagging the brake pedal .. since the engine will allow you to press the go pedal and the stop pedal at the same time you would still have Revs if this is an issue with the sensors in the pedal..

you might also want to read the computer and either turn the feature off and see if that changes anything or make sure the coolant and oil temp sensors are reading erroneous values.. if say in summer the coolant temp sensor things its 35 or 40 degrees when its really 60 then the system would likely arm.. im trsavelling (by plane) so I cant look and see if there is a setting temperature to trigger the system.. ive never known mine to activate in summer.. but maybe since in summer i usually load the engine down by starting the bus and turning on the A/C it warms up fast enough not to come on..

Desertsparky · 01-22-2023, 11:01 PM

It looks like it's electronic to my untrained eye and not an air system. Ill have to try some of those things when I get a chance. I appreciate your help.

cadillackid · 01-23-2023, 02:20 PM

the T444E uses electronic throttle it is not an air throttle system.
the engine is drive by wire

Booyah45828 · 01-23-2023, 03:45 PM

I'm with Christopher assuming it's cap functioning. I wouldn't worry about it.

It's only supposed to come on below 40°F. The fact that it comes on above that says that you might have a bad temp sensor which is causing it to come on when it's not supposed to. New trucks use an actual sensor to measure ambient temp, however something this old might fabricate that number from the manifold temp sensor, so use a scanner and see what those temps are. If the bus is cold and those 2 sensors don't read outside air temp then you found your issue.

I honestly wouldn't worry about it. CAP turns off when hitting the brake, gas, shifting out of neutral, or if the engine reaches a normal operating temp. It doesn't pose any danger to your kids/wife.

Dbacks2k4 · 01-23-2023, 07:32 PM

Yep it's automatic to help the engine build and maintain a safe operating temperature in colder weather. My first bus that did that startled me too, but it's completely safe.

You're probably better off leaving it be than disabling it or canceling it by hitting the brake or throttle switch.

Desertsparky · 01-23-2023, 11:47 PM

Yeah. So my wife just told me it didn't happen is summer. So yeah as usual my memory was wrong haha. Ill try those couple things to totally verify I just wanted to get ahead of it. I appreciate all the help.

rossvtaylor · 01-24-2023, 07:09 AM

Quote:

Originally Posted by Desertsparky

I appreciate all the help.

And I learned something new, from my non-help. Thanks, all!

jimmy649 · 03-05-2023, 02:05 PM

It idles up to keep up the oil psi. It's natural and good when it idles up to about 900...i think? Even if it goes to 1200, its ok. it keeps it juicy and healthy....If you don't like it, don't let it idle so long. If you are warming up your engine, it definitely means its good to go.

ermracing · 03-05-2023, 07:14 PM

Simple solution, use the cruise control - If you know you are going to
have it idle for a bit, when it's idling normally, flip the Throttle switch to ON and then press the SET button for a second or two and the idle will stay at the regular RPM.

Desertsparky · 03-05-2023, 08:17 PM

We took a short trip last weekend and we tested the theory about the computer. It was pretty dang cold for arizona but I had my son sit and watch it while it warmed up. It waited a fee minutes and then started accelerating. When he pressed the brake it went back to normal. So it seems to answer it. I am no longer concerned about it. I appreciate the help.

cadillackid · 03-06-2023, 01:30 PM

Quote:

Originally Posted by ermracing

Simple solution, use the cruise control - If you know you are going to
have it idle for a bit, when it's idling normally, flip the Throttle switch to ON and then press the SET button for a second or two and the idle will stay at the regular RPM.

yeppers this works to keep CAP from activating.. ive done it before idling in hotel parking lots early in the morning where I dont want it to race up and wake up the people still sleeping.. ill usually set it somewhere around 800 or so

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