I know this has been covered many times but I need help! I have a P0171 code that I can't clear. I have replaced the MAF, 02 (both), fuel pump, engine temp sensor, all OEM Denso. I also replaced the PCV. I replaced the T-stat with a TRD. I also checked for vacuum leaks. The code will not stay cleared. Has anyone had this same problem? What did you do to fix it?

check my thread out im going through the same issue.

clogged injectors maybe, you could try running a can of seafoam in the gas tank before a fill up. maybe fuel pressure regulator and/or clogged fuel filter also. worst case, it's the ecm.

i had this same problem with my 02 i replaced everything as well... i am not sure if you are, but i am running a CAI and the remedy was moving the MAF up on the intake tube closer to the TB. i dont know if that helps but another idea is get something to read your A/f ratio when mine had that problem i was seeing like 40.50:1 under load just some things to look at.

Did you check your fuel pressure after the pump change? Check for exhaust leaks before the O2? Clean your throttle body? Send your injectors off to Witchhunter for testing and rehab?

Thanks for the feedback on this issue. I cleaned the intake manifold when I replaced the MAF (denso), and I also replaced the fuel filter. I didn't check the fuel pressure, I'm sure I could but I don't know how, I've never checked fuel pressure on a Toyota. I do have a fuel pressure gauge that I used on my Ford F-150. There are no exhaust leaks anywhere I check that over thouroghly. I'm thinking that it could be a fuel pressure regulator or injectors. Those are the last 2 items remaining. If I hook up the OBD II what should I look at that would give me some sort of indication as to what's wrong? This P0171 code is driving me CRAZY! If anyone can help it would be greatly appreciated.

Here is the Service manual for diagnosing the P0171 on the 4Runner. I posted both versions, one for 49-State, and one for California. If you need any more info from the service manual let me know. I can print and post specific sections if you need them.

Attached Images

	A L L Diagnostic Trouble Codes ( DTC ) |Testing and Inspection, P Code Charts_ P0171, California.pdf (505.1 KB, 418 views)
	A L L Diagnostic Trouble Codes ( DTC ) |Testing and Inspection, P Code Charts_ P0171, Except Cal.pdf (464.6 KB, 358 views)

Thank you for that, I have that printed off from another post on this site too.

Fuel Pressure Testing on the 4Runner.

Attached Images

Fuel Pressure |Testing and Inspection, Component Tests and General Diagnostics.pdf (466.9 KB, 602 views)

Ok, so I replaced the O2 sensor (bank 1) with a OEM denso and check eng. light stayed off but today it popped on again. I used an Innova 3120LaT OBD II scanner to check the code and it came up P0171 AGAIN!! CAT & EVS symbols were flashing. I also pulled the freez frame data, it's as follows...
Fuel sys 1 - CL
Fuel sys 2 - NA
Calc load - 47.8
ECT (*F) - 190
STFT B1% - (-3.9)
LTFT - 37.5
Eng RPM - 2638
Veh Speed (MPH) - 67
IAT (*F) - 42

Can someone tell me what this means?

I changed my fpr then it went away.

have you checked and tested the wiring between the MAF and the ECU?

Update to this post.

So I worked down the list of possible causes to this P-0171 code from the cheapest fix on up. I recently replaced the FPR and no suprise to me, it didn't get rid of the code, it poped up very shortly after I cleared it with the OBD II scanner. I also checked the fuel pressure using a bango fitting and some creativity and the fuel pressure was within spec. (I wish Toyota installed a schrader valve on the fuel rail from the factory)

The only thing left to replace was the injector$$...

I looked at sending the injectors off for cleaning and inspection but decided not to due to shipping cost, down time..... Anyway, I bought new OEM injectors from Discount Auto Parts Online -- PartsGeek.com - Domestic & Import Auto Parts Warehouse and installed them. The result? Instant increase in power and, (knock on the dash) no codes. The power loss over a long time wasn't really notable, it ran great, didn't stall, stumble, get bad milage, smoke, use any fluids. I thought, especially after I installed the BIG tires, that was to be expected. But now the 4Rocker runs like it's near new.

I want to express my opinion about stuff you buy in bottles that you pour into your vehicle to fix its woes. As a means of preventative maintenance maybe... but if you have an issue that needs to be fixed, no amount of snake oil will fix your ills! The only thing that works is elbow grease and new parts. I spent the cost of one or two new injectors on 44K, Lucas, etc.... wasted money IMHO. This is pour advice! Ha ha ha... Leason learned!

My gut at the onset of this problem said fuel injectors but my long term plan is to replace the engine so now I know the fuel system is rebuilt too.

I want to thank the T4R members how offered their helpful advise.

Put down the seafoam and get to work.