Diagnostics: Engine Management Issues - P0174 & P0171

I realize this thread may be TLDR for some but wanted to provide detailed info about the engine management issues I am having with formerly P0051, now P0174 and P0171 DTCs. I put together a table of the DTC history along with another table with symptoms and maintenance activities. In general, it always seemed to me that the basic maintenance items with chemical cleanings etc managed to bring the engine just enough within the range of operating specs to keep the engine management issues in check. When resetting the computer by negative terminal removal, the computer usually struggles to relearn - almost as if it is correcting for a lot of parts in an aging system.

It started with a P0051 occasionally interspersed with the P0174. I also had vacuum leak codes that were fixed with a replacement OEM fuel cap followed by a smoke test along with a few other items in the chart below. I believe the smoke test helped when the tech open and closed various valves and solenoids in the vacuum system and allowed pressure to build up at various points in the system. I always felt that by kind of working and stretching the system that performance was improved.

Two main points of influence are high ambient temperatures and inclines [either vertical or horizontal]. I recently replaced the upstream Bank 2 Sensor 1 with an Denso direct fit replacement. This removed the P0051 but added the P0174 and P0171 DTCs. The P0174 had previously appeared along with the P0051 in 2 out of the 9 reports. The P0171 is a new code added since the upstream Bank 2 O2 sensor replacement in June.

I bought both upstream sensors for replacement based on the Rock Auto recommendation to replace both banks to avoid engine management issues. That made a lot of sense to me. I later learned of another school of thought on this site to replace both sensors (upstream and downstream) on the affected bank. I have looked at the upstream sensor on my 04 AC and I don't see any way to get to the connector unless removing a few things in the way such as power steering tubing. I had hoped to replace the Bank 1 sensor when replacing the steering rack this fall. Currently, after replacing the upstream Bank 2, I am showing no O2 sensor codes.

Additional Items: 227k miles, Original MAF sensor, Original Coils, OEM timing belt [including WP, gaskets, crank and cam seals, etc] replacement 8.5 yrs and 61,000 miles ago. Also, the engine had a lot of idle time over a 5 year period since the timing belt change in Dec 2016. This makes me lean toward the possibility of dirty injectors, although I did not have significant sludge or varnish build up in the valve covers during replacement last August.

With 10 straight 90 degree plus days and forecast in the 90s every day through the end of the month, my engine is suffering.

I am hopeful that someone who has knowledge or experience with these codes and issues could help me to narrow and focus on the diagnostic steps in order to fix these problems. I printed out the Diagnostic steps and chart and am looking them over now. Anyone recognize what is the likely culprit here?

 

Do you have the means to read live data ?
That's a lot of MAF cleaning for such a delicate component but live data of actual MAF reading would tell something.

 

No, I don't, unfortunately, and I can't afford an Autel because I am trying to finish up with my suspension parts replacement. It would be a stretch, anyway.

 

Maybe there is a more affordable option that I could swing, if push comes to shove? I am still trying to recover after numerous hospitalizations over the fall and winter.

Generally, I try to save and buy once...that applies to OEM parts, tools, and supplies. I might know one guy who could take live data. I take it that would be very useful.