P0171 issue

Hi Guys,My 2000 manual trans with CAL emissions with 135k miles showing P0171 code. "System too lean,(AF lean, bank 1)". I have changed MAF and upstream O2 sensor. Cleared code, then it reappeared after 4 miles on uphill test run. Hoses seem ok. It starts and runs smooth but mileage seems down. My google search shows it could be, fuel filter (has original), vacuum leak, fuel pump, downstream O2 sensor, pcv valve, injector fouled.
Any experience with clearing this would be appreciated. Thanks.

 

Did you keep your MAF & O2 sensor that you removed? And did you replace with OEM or at least Denso?
What is the status of your hoses? Ever been replaced in total? They're 24 years old potentially. Get a mirror and inspect the under sides of them. Also pay attention to any of them that attach to plastic parts and check those attachment points for integrity also.
Have you recently done any work that would require intake removal? You can try a smoke test (see you tube) or spray around the hoses with a) starter fluid which will cause the engine to race if it gets pulled in but runs the risk of catching your engine bay on fire if you get careless b) water mist which will cause a stumble and can harm electronics if you get careless.

Fuel filter. Probably not the cause, but cheap and easy to change and at 24 years, what the heck, let the poor guy retire. Unless you live in rusty land...then proceed with caution, because again, that probably ain't it.

Injector, could be but that would more likely produce a misfire code. Plus you're kinda low mileage for that.

I'd focus on the vacuum lines.

 

Kept old parts. Replaced with denso. Also replaced one small hose that was cracked. Inspection of others looked ok but old. Will try the carb cleaner test next for unseen leaks. Thanks

 

Good luck and be careful

 

I'd also look at the downstream sensor. Upstream ones don't seem to go nearly as bad as often.

 

Final results: Changed MAF with denso purchased at ebay site with good feedback, still trip a code. Then upstream Oxy, then downstream oxy, then fuel filter. Tripped a code after each swap. Finally bit the bullet and took to Shop. They did smoke test and found no leak in system. They tested new MAF and showed poor readings, suggested changeout even though it was new.
Took it home and installed the expensive "Toyota" Denso MAF. Passed smog no problem. Most work i've ever done on this car. Thanks for the input on this.

 

Awesome, glad you got it sorted.

Can we all agree that the Ebay\Amazon parts are cheap garbage counterfeits?

You MUST get the sensors from a dealer.

https://www.toyotanation.com/threads/counterfeit-toyota-parts-exposed.1693280/

https://www.toyotanation.com/threads/psa-fake-toyota-parts-on-ebay-amazon.1675488/

 

Filed under "Lessons Learned". This was costly in time and parts. Oh well. thanks again

 

Glad to hear you're up and running.

 

Thanks for the follow up. Hopefully your “lesson learned” will keep someone else from going through it.