Engine/Transmission (1998.5 - 2002) Cruise control and dead pedal!

[Chavez]

Starting, i have a 2002 3500 4x4 six speed 165,000 miles with no performance mods. When ever i use the cruise control on the freeway for a period of time then come to a stop the idle has elevated to 900-1100. Then sometimes when i go to take off from a stop let the clutch out the truck stalls, not driver error but like the engine is not excepting the load... . something with the computer or pump. This happenes a majority of the time, also when this is happening the ABS light will come on and go off just fast enough to catch my eye. But never stays on. when i shut the truck down and let it sit for a minute and restart it... idle is back to normal until i use the cruise again. I tried to see if it is when the cruise is on or when it is set, only seems it does this when the cruise is set. No CEL or codes, except twice with dead pedal. Using cruise for about an hour exited freeway canceled cruise went to hit acc pedal started to accel. then went dead with CEL. Pulled over hit the pedal afew times nothing. Shut truck off waited about a minute, started again hit pedal twice nothing... third hit she was alive again and ran fine with CEL and codes 1693 and 121 low voltage apps. After a few days of driveing the CEL goes off. I checked the voltage for the apps and was a little off . 493, readjusted and set to . 515. Still get the high idle after cruise is used. Anyone have an idea?

Also this is a different problem i think. It feels like the truck surges at mid RPM range, had cummins and dodge drive it and they said they could not fell anything. Me driveing it everyday i know that its doing it... very lightly but it is. No codes. Should i try to reflash ECM?

 

[MMacklin]

When this happens turn the key on & off 3 times this resets & clears the computer problem you will be good to go

sounds like you have a throttle positioner problem (sensor)

 

[PC12Driver]

With the elevated idle, occasional dead pedal, 121 code, and surge at mid-rpm all point to a bad APPS.



The APPS is basically like a volume knob on a radio, as you move the pedal the resistance changes, thus changing the output voltage. And you know how old radio volume knobs get "scratchy" over time? Same thing with an APPS, but instead of noise over the speakers, you'll get fluctuations in RPM. And the first place for it to wear out is where it spends the most time, so that's where your slight mid-rpm surge is coming from. The cruise control in your truck bypasses the APPS, so if your surge goes away with the cruise on, then that points to the APPS as the source of the surge.



The APPS also has a idle verification circuit. Basically, the APPS sends a signal to the ECM when the pedal is at idle. This helps the ECM "learn" the voltages of the APPS (more on that in a sec). When you turn on the key and the pedal is at idle, the ECM reads and memorizes that voltage as idle. Drive for a while and take your foot off the pedal, the ECM will get the at-idle signal, and if the voltage doesn't match the idle voltage that it remembers from startup, then it will throw a code. So when you have your 900-1100 rpm idle (as a result of a higher voltage from the noisy apps), and then power cycle the truck, the ECM will learn this new, higher voltage as the new idle voltage. If the crud in the APPS clears up and the at-idle voltage goes back to something lower than what the ECM memorized, you'll get the 121-APPS low voltage code.



I've replaced two APPS; one at 80k miles due to the surge and one at 125k miles because of the high idle and dead pedal you describe. I'd say at 165k, you're due for an APPS. See this thread for your options.



Incidentally, adjusting the APPS voltage on a manual truck doesn't do anything except maybe move a dead spot around. As I said, the ECM self-learns the APPS. Turn on the key and it learns the idle voltage, slowly depress the throttle to the floor and it learns the maximum voltage, and that's it. But the PCM in the auto trucks need to see the correct window of voltage from the APPS to control shifts and TC lockup at the correct speeds. So don't waste your time chasing APPS voltage on your 6-speed.



Not sure what's up with your ABS light or the truck stalling though. I don't think the APPS would have anything to do with the brakes, and the ECM would still try to keep the rpms over 850 regardless of the APPS voltage when launching. We're you giving it throttle when it died from a stop?

 

[Chavez]

PC12driver thanks for the response. No, when the truck stalls from a stop i am not giving it any throttle. Usually letting the clutch out from a stop it just pulls itself along. But when i am having this high idle problem i start letting the clutch out and it dies as if it had a load on it. But is kind of weird the way it dies is so sudden. . not really giving you a chance to try and catch it with the clutch. More like as if you shut it off at the key. As far as the ABS light it seems that it only does it when the high idle is happening.

 

[darkhorse]

With the elevated idle, occasional dead pedal, 121 code, and surge at mid-rpm all point to a bad APPS.



What a great post,PC. Thanks.

 

[johncameron]

I don't think it's related but when my cam sensor went bad I had no Idle torque and th etruck would stall taking off without giving it tome throttle.

 

[Alexdring]

Where is a good place to see how much an APPS would be. Looks simple enough to replace after reading the manual.

 

[darkhorse]

Where is a good place to see how much an APPS would be. Looks simple enough to replace after reading the manual.

See post #3 above.