System running rich. Random check engine light, P0172 (pending) / P0175 (current)

[tahoe_toronto]

Hi all,

Long time reader here, first time poster. Big fan though

I am stuck trying to figure out P0172/P0175 that are coming up once a week after reset. Before I go poor swapping parts I figured it may be a better idea to see what the pros here think Basically, I am stuck what should my next step be (try stuff, go see a mechanic, etc).
I got the truck (Tahoe 5.3L 2018 200km) two months ago and some things got fixed (suspension, transmission), but p172/p175 has been there since the start.
After an hour of drive it would have up to 20 misfires per cylinder.
I changed the air filter. The old one was the most clogged filter I've seen ever. I also changed the spark plugs since it didn't look they were ever changed. I cleaned the MAF.
This dropped the misfires to 0-5 per hour of drive. They are random at random cylinders, one drive it would be max misfires on cylinder 8, then on cylinder 3, etc, there is no pattern.
I am no expert at this, but have my cheap BT OBD tool has some data I attached here. Also on

https://imgur.com/a/GPc2U4J

Basically:
Idle
If left longer than few hours, engine always starts at 1.2k RPM and then goes down. I read that this should be to warm it up, but it was happening even on a hot sunny day 30+ degrees (90 F). Should it be this way?
**MAF: I am assuming the MAF works? (Maybe it's going bad, how can I tell?)**MAF at idle: 3.6 g/sMAF at car off: 0Disconnected MAF: All bunch of error codes including P0102
Fuel:
Ethanol 10.6% (somebody mentioned it may be that in the fuel)Usually filling 87 octanes. Last time fillled 93+. Nothing changed muchUsed: Chevron Techron Concentrate Plus Fuel System Cleaner. Nothing changed.
Vaccum at idle with AC off -21Vaccum at idle with AC on max -18
**Fuel trims, in the negative, a lot.**At Idle with AC off: -19.5At Idle with AC on max: -8 -10
Where do I go from here. Some internet chats are pointing to high pressure fuel pump (and some are saying it is not present on this truck) so I included that data from the OBD, but not sure how to gauge it.
What should I do next? (Continue down the rabbit hole, check Evap system and how? Check vacuum, visit a mechanic and get them a free TimHortons coffee as a bribe? )

 

[Fless]

It's taking away fuel (negative fuel trims) so it's either getting too much fuel or too little air (or so it thinks). You stated one value, though; was that for one bank or are they both essentially the same?

What are the short term trims (both banks) at idle and at, say 1500 or 2000 rpm?

Has the throttle body been cleaned lately?

The MAF reading seems a bit low, can you graph it along with the rpm and run it from idle to 1500 rpm or so to see how much it changes?

 

[tahoe_toronto]

Thanks for the reply.

About the Trims:
Both banks are about the same.
On idle, short ones are around 0 to 2% B1 is about 1% higher than B1 on and off. If the car doesn't move, at 1500, B1 is -3% and B2 is -6%

If I am starting from zero, at acceleration near 1500, B1 is -2%, B2 goes to -8%. Then down to -14% for both sometimes. Long ones are from -8% down to -21% accordingly.

It seems that above 20km/h short ones move around from 10% to -10%, but long ones move between -7% down to -22%

Throttle body:
I haven't cleaned it so far, and looking at the condition of the drive train, I doubt it was ever cleaned.

MAF:
I'll get the graph and reply.

 

[tahoe_toronto]

Here's the graph. I didn't know a better way so just pushed the pedal down in 100RPM increments, and read the numbers eyeballing what they averaged to the best I could.

 

[tahoe_toronto]

I cleaned the throttle body (lots of deposits) and the numbers are better.

I noticed the truck's trims ends up in two cases:
Idle after ignition stabilizes and is great, idle after short drive is a bit worse off.

What do you suggest, do I continue hunting this down or is it good enough now?

The numbers are:

Idle few minutes after ignition, if the car has been sitting off for a while.
Short B1: -1.5% to 0, B2: -0.5% to 0.5%
Long B1: -2.3% B2: -3.9%

After a 5 min drive around, then rest for few minutes, idle ends up at
Short B1: -4% to -2.5%, B2: -2.4% to -0.7%
Long B1: -10.2% B2: -11.7
For whatever unknown reason, on idle after a short drive, the Throttle Absolute position went down from 17% to 13%

 

[Fless]

Can you get a scanner on it that will reset the fuel trims? I think that the LT trims are going to take some time to adjust since they're learned from before, and resetting them would start them over with the new condition. (STFTs reset with ignition cycle; LTFTs are learned and stored.)

If not, they should come down over time as long as the ST trims stay low. Anything under +/- 10 is "okay", but +/- 5% should be attainable with everything working correctly.

Keep your eyes on them for a while, see what happens. We'd love to get an update later on, good or bad.

And your throttle body position is relearned with a few driving cycles, so expect that to change a bit. Cleaning it allows the butterfly to fully close.

 

[tahoe_toronto]

It looks like I will be driving for a bit until they stabilize sadly. I am a bit embarrassed to admit that my scanner is a cheap $20CAD BT (Veepak something) from Amazon. I am trying to see what would be a good scanner for the truck, as I plan to keep it for a long time and it has a lot of electronics in it. I was looking at Innova but still searching for something under $1k.

Keep your eyes on them for a while, see what happens. We'd love to get an update later on, good or bad.

Definitely. Also, thanks for the help. Cheers!

 

[Fless]

Depending on which one an auto parts store has, you may be able to use theirs to reset. There's a Tech 2 Owners Map thread on here that has a list of some of our Tech 2 owners; if one is nearby I'm sure you could get it done. But any good capable bidirectional scanner should do it. Come to think of it, I need to see if my Autel will do it.

 

[swathdiver]

Depending on which one an auto parts store has, you may be able to use theirs to reset. There's a Tech 2 Owners Map thread on here that has a list of some of our Tech 2 owners; if one is nearby I'm sure you could get it done. But any good capable bidirectional scanner should do it. Come to think of it, I need to see if my Autel will do it.

Unfortunately the Tech-2 does not work on the K2s. I think the OP needs to keep cleaning the throttle body, inside and out. Since the negative trims have lessoned, I've ruled out a vacuum leak in my mind.

@tahoe_toronto Sign up for the shop manual at AllDataDIY so you can follow the troubleshooting guide for those codes.

 

[Fless]

Unfortunately the Tech-2 does not work on the K2s.

My mind was way out of context!