Dies at idle after a couple minutes

[jlamp67]

I have been trying to figure out why my gen 4 - 6.2 won't idle consistently after a cold startup. This is a stock L99 with a BTR truck norris cam, (no vvt or dod) and is in a Jeep that runs great at operating temp and after it is at operating temp it idles ok, but shortly after startup as the idle comes down the idle is very rough and eventually it will die. This is with no throttle input. I have tried lower idle spark and have tried adjusting idle airflow but that is about all I know to try. Would appreciate it if someone could look at my log and tune and give me some tips. I know it should idle better than this even with this cam and it does seem to be temp related.

[RDF1]

Have you done any fuel tuning?

[jlamp67]

Yes, this was professionally tuned a month ago and LTFT's stay right at around zero at all times and drivability is otherwise great. I feel it was well tuned (but I know little), as I can see he touched everything and it runs great otherwise but the cold idle is something he may not have noticed in a tuning session and it doesn't do it when warmed up.

[blindsquirrel]

When it goes closed loop, the trims pull out all the fuel. But you didn't log the O2 voltages. Get another log.

[blindsquirrel]

LTFT's stay right at around zero at all times

screenshot.13-04-2025 12.16.53.png

[jlamp67]

Sorry, I meant near 0 when cruising or normal driving, not when its doing this thing at idle. I have added the 4- 02 voltage PIDs and here is another log

[blindsquirrel]

O2s are not working, they're flat at the bias voltage and don't react to any fueling changes. Well, they drift up towards ~550mV, but they both track right on top of each other, identical. Dig in and diagnose why the O2 signals aren't working. Unlikely to be bad sensors, it's rare for two parts to fail at the same time in the exact same way. The cause will turn out to be something they both have in common. This is not a tune issue, it's a part or wiring failure.

[jlamp67]

Well, guess I better get the meter out and check those circuits. This is a newly revised harness from my Jeep LS swap guy and we did have a couple other issue with it on the Jeep side but I sure would have thought the GM side would have been correct.
I appreciate the info and will see what I can figure out.
Thank you.

[abc]

Looks to me like it just needs proper fueling during the warm up phase. Show us a log of it in closed loop idling.

Based on the stored LTFT's something is not happy. We should probably see the .HPT file also.

[blindsquirrel]

Both O2s are dead and don't respond to rich/lean. As much as the trims are pulling out, they should both be pegged down under 100mV. They don't drop even though trims take away enough fuel to stall the engine.

[Alvin]

I would take the time to check fuel pressure too. especially since this is a swap.

[jlamp67]

Ah Mr. Squirrel, you are not so blind! I went out and found the bank 1 front O2 harness had not been secured correctly and had hit the exhaust manifold and fried all 4 wires together causing the behavior you noticed. Spent some time getting that fixed and after did a cold start (no laptop with me to log with at the time) and it idled just fine, didn't die. Also took a drive and it runs pretty good down the road. I will get another log tomorrow from cold start and post it here. Interested to see if how it is now looks good to others or if anything can be improved on the "truck Norris idle."
Thanks for the suggestions.

[blindsquirrel]

So wiring to one sensor took out both of them? Did both sides come back to life after the wiring was fixed? Just asking because that's really weird, one side shouldn't be able to affect the other. The only thing they share is the heater fuse and the ECM.

Speaking of heater fuse, make sure to check that. Melted wires and all...

[jlamp67]

The heater fuse was in fact blown. I have attached the tune and a short drive from startup/warmup. Does not die at idle anymore.

[edcmat-l1]

VVE mess.jpg

Might not be stalling anymore but definitely could use to be properly tuned. VVE is a mess at idle and right off idle. First sign the "professional" was quite.