P0172 and P0175

[CJchevy]

Hi Folks,

New here and I hope somebody out there may have some insight on this problem I am having.  2014 Silverado, 4x4 5.3l

The issue popped up for the first time last spring not long after replacing the original air filter.  Engine stumbles in second and third gear, not every time though.  Throws a p0172 and p0175 on occasion and the code clears after a day or two.  It did this a few time last summer then the issue vanished until just recently.  The same two codes popped up again.

I have since purchased an Autel scan tool so I started collecting data and here is what I can share with you.  All freeze frame data shows the codes set at idle only, engine warmed up.  The LTFT's are off the charts at idle only and they recover back in range (within 5 %) while driving or depressing the accelerator.  As the LTFT's revert back to normal, there are no misfires and the engine runs perfectly fine, plenty of power.

I looked at all these items and they all check out in range:  MAF, Baro, ECT, IAT, MAF, LP Fuel pressure, HP Fuel pressure.  I tested the evap purge sol and confirmed it does not leak and I have inspected the PCV circuit and confirmed it is operating correctly.  I performed an injector balance test and that looks good to me also.

Convinced this is not a fuel delivery problem, I started looking for an intake restriction.  I pulled the throttle body and it was filthy (115000 miles).  Cleaned her up, and did a throttle re-learn and bingo! LTFT's near zero on both banks... Truck runs perfectly... for two days.  I am right back where I started from.  My LTFT's are -30 at idle but recover as you press the accelerator and I am getting misfire counts on all cylinders except #8.  These misfire counters are mode 6 data, the GM specific data does not show these misses, however, it does count a few but does not specify which cylinder.

I wonder if the aftermarket air filter element is causing a restriction.. The airbox is not modified, the filter element is a fram.

I would love to get some more insight into this.  Also, I am not going to fling parts at this either without proving a failure.

Anything I may have missed?  

[eppieguy]

You'll get much better help in the K2 forum, this is the T1 forum which is 2019 trucks.