Engine/Transmission (1998.5 - 2002) Strange Idle

[JWelch]

for the last few weeks I have been having a weird idle after my 1 1/2 hr drive to work. after I get off the highway and stop the truck will idle up to almost 1100 rpm and stay there. It used to go away if you shut the truck dow but now it comes back if you shutdaow and wait a little while. But after a 10 hr shift and the drive home nothing. Then this morning it started to do it again but onle to about 900 rpms.



Any help will be greatly appreciated.

 

[PC12Driver]

Mine was doing that the last time my APPS went out. Any codes?

 

[JWelch]

Got em this morning: 1693 and 234(overboosting)



Haven't checked yet. Will though soon.

 

[JWelch]

anybody have any thoughts

 

[JLandry]

What year truck are we talking about and what modifications do you have?



I suspect the P0234 DTC (Boost Limit Exceeded) might not be related to the idle rpm problem. The idle rpm issue sure sounds like a problem with the APPS.



Best regards,



John L.

 

[JWelch]

2002 2500 4x4 6 spd w/ 85k miles

 

[JLandry]

Well this is a tough one.

I'd start by clearing the DTC's if you haven't done so already to see of that P0234 comes back. But I don't think it's related to the high idle... it's probably just a coincidence.

It sure could be the APPS acting up. One way to trouble shoot a flacky APPS output would be to buy a ScanGauge so you could monitor what the ECM sees the throttle position as being (percentage). If you were sitting there at idle after your commute and the ScanGauge showed the a throttle position of something other than zero percent, you'd know right away something was wrong with the APPS output. If the ScanGauge showed the throttle position to be zero and the engine was idling high, then it probably couldn't be blamed on the APPS.

Something you might try first is to have the ECM relearn the APPS voltage range...

Disconnect the negative battery cable from both batteries then turn on the headlights for 10 or 15 minutes, then reconnect the battery cables.

Turn ignition key on but don't start engine.

Slowly press accelerator pedal to the floor.

Slowly release accelerator pedal.

Turn off ignition key.

If you did have to replace the APPS, the cheapest route to go is to replace just the throttle position sensor which is bolted to the side of the large cast aluminum APPS bracket. Williams Controls makes a sensor that fits and works perfectly, but it needs a wiring harness adapter to plug into the truck wiring harness. Forum member Timbo sells a kit which includes the sensor and the harness adapter for a reasonable price. You can send him a private message for details.

Best regards,

John L.

 

[JWelch]

Appreciate it and I will try to do the reset on friday morning. I cleared codes less than a week ago and the 234 was there. It came back when I checked it over the wknd.