nikovdh

1999 Lexus ES300 - 162k miles
This recently started popping up a few weeks ago. This last week I did a bunch of replacing of parts due to VVT malfunction codes and that P0171.
Replaced:
Bank 2 A/F sensor (Denso)
Bank 1 A/F sensor (Denso)
*Did not replace Bank 1 downstream heated 02 sensor*
PCV valve (OEM)
OCV bank 2 (OEM)
OCV bank 1 (OEM)
Air intake tubes (the 2 smaller ones after the MAF) due to crack line near the ends

My car now runs better than when I bought it 30k miles ago.. but yesterday after driving home from work.. and while on the freeway... the p0171 came on again.
I've been researching the heck out of it the past 2 weeks. My car has no symptoms of a lot of the things like fuel pump issues, etc. My car feels literally perfect right now, which is what baffles me about it.

I have some pictures attached of the freeze frame data during that recent p0171, and then live data of idling the next day outside my place after a short trip to the store and gym.

I'm pretty inexperienced with what all this data means, ,so if anyone else has any clue and it seems to enlighten you on my issue.. please leave a comment.
If you have any questions that may help, please ask

Note: the Live Data seems to have more available data than the freeze frames..

nsghtbrwry

Fuel trims are your key. Almost certain that you have a huge vacuum leak, with nearly 40% positive LTFT

EDIT: Listen for hissing/sucking. Spray carb cleaner around hoses/vacuum line connections to see if the idle rises. If it does, you found a leak

nikovdh

hmm.. dunno about that. I just watched some very informative videos on Fuel Trims. My Long term fuel trim is close to zero at idle.. increasing RPMs is what causes my long term fuel trims to increase. Apparently this is the opposite situation of what a vacuum leak presents. (Vacuum leak has high Long term fuel trims on idle, and a more normal condition as the RPM increases due to the increase in metered air as a total % of air entering).

So it seems my data presents a situation that is more indicative of a dirty/malfunctioning MAF or a fuel delivery problem.
Both banks are increasing Long Term Fuel Trim at high RPMs, even though the code is only giving me a code for 1 bank.

nsghtbrwry

Cool, that makes sense. I'd nab a MAF from the Pick-n-pull and clean it with the right spray, then try that

fortitude

Additional resources
Toyota TIS - 2 day access for $15(?). Full Tech Manual. Was able to down load the pages and save - not sure if that has changed though.
The manual gives in-depth analysis and step by step processes to diagnose and repair.
https://techinfo.toyota.com/techInfo...l=ti_home_page

Also found a multi-meter & test light good tools to have on hand when diagnosing.

nikovdh

Cleaned my MAF this morning. Have it drying all day (not plugged in) but I'm gonna drive in a couple hours and see if any difference in rising Long Term Trims when accelerating.

Any suggestions as far as good quality budget multimeters / test light?

I intend to subscribe for a 2-day Techinfo Toyota on my days off so I can spend all day and night downloading the manual pages lol.

fortitude

If you have not already removed the negative cable from battery terminal, i suggest you do it first, then re-install MAF, then reconnect negative cable to battery. I believe this will also delete the stored fuel trims allowing the computer to "re-learn" especially with the parts you have recently changed.

Multi meter - Sears/Craftsman (was on sale)

Test light - Harbor Freight - I purchased the centech "computer safe" logic probe. Read up on using test lights so you do not fry your ecm.

Downloading was fairly quick, it was the collating that took time...... Define a system to name each file so it will be easier to merge later.

Also, watch Eric O from South Main Auto videos on youtube. His electrical diagnosis skills are excellent. He tests his assumptions thoroughly PRIOR to replacing any parts.
Scanner Danner and Schrodingers Box have good videos on fuel trims, O2's, etc.

nikovdh

Schrodinger's Box had the videos that really explained fuel trims really well to me the other day. I've started watching some of his other videos too.

On a side note.. after cleaning my MAF, my long term fuel trims have dropped down to about positive 5-6% during acceleration (have been driving around with scan tool in my right hand lol), down from 30ish% before cleaning, so it looks like the dirty MAF was the culprit. I did not reset the computer by disconnecting the battery. As far as I know, it automatically adapts. I did however disconnect the battery while taking out the throttle body to clean it and install the new IACV. That was on Saturday though (looks like I forgot to mention the IACV in the initial post lol)

Very rewarding to tackle this stuff on your own!

nikovdh

BTW, here is a picture of my old Idle Air Control Valve unit. I might have been able to just clean it.. but it just felt like a big task to get the throttle body off (first time is always so intimidating!), so I wanted a guarantee that it would work out.. and I've heard a new one will be a more long term solution. Cleaning it without taking it off the throttle body didn't work for me when I tried it.

fortitude

See if your scanner is capable of reading readyness monitors and confirm they have been "completed"

nsghtbrwry

When you put the new one on, use hex cap (Allen) bolts instead of the stock JIS screws. Make it much easier to take off in the future, those JIS screws tend to strip at the drop of a hat