Idle flare up 100% stock 5.3

[bk2life]

Gents,

customer of mine has a bone stock 2007 4.8 truck.
it is his work truck and lately it will raise the idle from 550 to 1300 rpms for what appears to be no reason.

it wont come down until ignition is cycled and engine restarted.

for testing we installed another throttle body and maf off another exact same truck (same part numbers ect) and it does the same thing.

i dont have a copy of the tune, but it is not modified in anyway, but i do have a copy of the log.

i have used special functions and tried 'relearning' the throttle body with no luck.

when the idle increases, i can not over ride it. it will stay at a high idle until restarted.

zero check engine light, or codes stored.

any ideas to try or comments greatly appreciated as id like to help get my friends work truck serviceable again.

thank you.

[Alvin]

There was a similar thread not long ago and it had to do with the alternator. Verlon found the issue in the backend.

[abc]

I vaguely remember that also and I think similar to that one, the PCM reported voltage is very low at idle (12.5 volts). Since you have a donor parts truck, try the alternator?

[verlon]

customer of mine has a bone stock 2007 4.8 truck.
it is his work truck and lately it will raise the idle from 550 to 1300 rpms for what appears to be no reason.

it wont come down until ignition is cycled and engine restarted.

That's not idle boost. Idle Desired RPM stays low, but actual engine speed climbs very high.

Looks like idle airflow control loop is going into failsafe mode (integrator is disabled and straight BRAF is used), but there is no way to get why PCM is doing so.

[Alvin]

Post the tune file. I didn't realize it was raising by that much.

[blindsquirrel]

My initial reaction would be, if this is a stock engine with all stock parts, and a stock tune file (it is, I checked VIN/IDs/CVNs), and it does something this weird, then something is broken and it's not gonna be fixed with tuning anything. Treat it the same as if you were a tech in a dealership.

[Alvin]

My initial reaction would be, if this is a stock engine with all stock parts, and a stock tune file (it is, I checked VIN/IDs/CVNs), and it does something this weird, then something is broken and it's not gonna be fixed with tuning anything. Treat it the same as if you were a tech in a dealership.

I was thinking it was a case of "all stock" but had some wild idle settings changed.

I've been lied to on here before.. lol

[blindsquirrel]

Shore would be nice if all the ETC PIDs were in the log, like the APP stuff, and raw voltages for all 4 sensors if those are available. May have to use a real scan tool to get to some of that.

edit: I wouldn't have thought it would be possible for it to do something like this without setting a code. Most of the ETC stuff is First Error, too.

[bk2life]

Post the tune file. I didn't realize it was raising by that much.

, if this is a stock engine with all stock parts, and a stock tune file.

Looks like idle airflow control loop is going into failsafe mode (integrator is disabled and straight BRAF is used), but there is no way to get why PCM is doing so.

Shore would be nice if all the ETC PIDs were in the log, like the APP stuff, and raw voltages for all 4 sensors if those are available.
.

I’ll stop by his house and download the tune.
Yes, it is 100% stock file, truck, exactly how it rolled off the assembly line.
Ill add another log with ETC pids.

What is APP?
And to clarify what 4 sensors?

Thank you

[gtstorey]

APP= Accelerator Pedal Position

[Boosted Rooster]

I have seen where the throttle body idle air flow learned values have changed over time due to carbon buildup. Google PIP4578B. Even after cleaning, the ECM can "burn" this value in and any scan tool learn functions like the Idle Learn are not successful. Sometimes a battery disconnect and an ECM recalibration/program fix it, other times the ECM requires replacement.

[blindsquirrel]

Throttle Learn - Document ID 1820246.pdf

[bk2life]

,,,,

thank you for that.

the owner feels this is what he has to do, and has done.
he says the flair up has been gone for several days now.

i have not been around the vehicle to download the tune, but, im going to guess its all ok now.

wierd, but, thats how the cookie crumbles sometimes.

thanks to everyone for the help and ideas

[Fast4.7]

I was thinking it was a case of "all stock" but had some wild idle settings changed.

I've been lied to on here before.. lol

I ran into some pretty big idle changes a few years ago that made me believe the file had been manipulated. NOPE, GM did it. The GMC and Chevy versions of the same engine and same vehicle had large differences in the calibrations. I had the stock tune file pulled from GM and flashed to the PCM and it had the same changes from the equivalent Chevy. They were both stock GM Express/Savanna work vans with 6.0Ls. The GMC had some weird idle problems. Changing to the Chevy tune file corrected the issues. The idle in the GMC would flare up on coasting deceleration as the transmission downshifted, then take twice as much brake input to bring it to a stop and was eating brake pads two times as quickly as the Chevys.