4Runnin2000
New member
http://www.rockauto.com/m/mobilecatalog.php look here for it if you are going to replace it. $72
P0171 Lean bank 1 Question
- Thread starter jhueter
- Start date
It should stay running even if the MAF is bad, it'll just run like hell. Sounds to me like a bad fuel pump, that is what was wrong with mine with a P0171. It had symptoms of a bad MAF,drove to the junk yard to grab a new MAF for $20. as soon as I got block away from the yard it fell on its face and didnt even want to limp there. Got it there and changed the MAF with two others and still no bueno. It ran but as soon as i gave it gas, it wouldnt move. towed it home and the next day it wouldnt start, Fuel pump went bad.
That's what I'm thinking now. I checked the plugs and they were fouled badly. Changed them, still nothing. Opened the fuel line in the engine bay near fuse box, no spray and bone dry. Just got done swapping the fuel filter hoping that was the issue, still no change. Fuel pump should be here tomorrow from Rock Auto. Will be dropping the tank Saturday. Sprayed down as many bolts as I could get to with PB Blaster the other night. I just love living in MN with all the salt they put out.
And I've never done a fuel pump before, let alone dropping the tank. Not looking forward to it.That's what I'm thinking now. I checked the plugs and they were fouled badly. Changed them, still nothing. Opened the fuel line in the engine bay near fuse box, no spray and bone dry. Just got done swapping the fuel filter hoping that was the issue, still no change. Fuel pump should be here tomorrow from Rock Auto. Will be dropping the tank Saturday. Sprayed down as many bolts as I could get to with PB Blaster the other night. I just love living in MN with all the salt they put out.
Its pretty simple I never did either. I suggest getting to the access panel under the rear seat and disconnecting it and testing it first. I used jack stands to suppport the tank until I put the jack under it to lower it down. It intimidating until you start doing it and realize there isnt much to the system.
Couldn't get the rusty bolts loose, so took it to my friend's shop. He got the fuel pump swapped out. It's a Denso from rock auto parts. Driving home and about 15 miles down the road on the freeway, it starts lurching again. Was not liking it when I gave it more gas. Now I can't get it started. Just keeps cranking. This is driving me nuts.
To summarize, P0171 was the code, cleaned then replaced the MAF. Then changed the fuel filter. Now the pump. All vac lines are hooked up. No CEL right now. What else can I look at?
To summarize, P0171 was the code, cleaned then replaced the MAF. Then changed the fuel filter. Now the pump. All vac lines are hooked up. No CEL right now. What else can I look at?
Hesitated and stalled on the way home from the shop at around 20 miles. Towed it home. Decided to order another fuel pump, thinking I got a defect, and planned to remove the tank again in a few days. But in the meantime, I decided to try a couple bottles of Heet to remove any water from the gas. Put that in, alt with a few gallons of gas and let it sit overnight. Next day, it fired right up. Put a full tank of gas in and ran about 50 miles of city driving. It sputtered a few times, but didn't stall. It must have been a bad tank of gas. The shop that dropped the tank and installed the fuel pump should have emptied the tank and put fresh gas in, but oh well. I'm just glad my truck is running again!
Still running rough occasionally on this tank of gas, and I'm halfway through it. Forgot to mention I used the mid-grade octane (89) hoping it would help. Also randomly throwing up a P303, cyl. 3 miss-fire, when it does run rough. And the CEL will either flash, or stay on steadily for a little while, then go away. Going to check the plug wire for cylinder 3 as I did change the plugs when I was chasing the original issue. Also going to put some seafoam in and top it off with 87 octane.
astronut203
New member
New MAF Suggestions
So it looks like it comes down to a bad MAF and I'm in need of replacing it. What's the suggestion for a new MAF? I have seen a lot of names thrown out there and there is a wide range of the prices.
So it looks like it comes down to a bad MAF and I'm in need of replacing it. What's the suggestion for a new MAF? I have seen a lot of names thrown out there and there is a wide range of the prices.
AntonioCm1983
New member
Problem is I'm having same code pop up but problem is I replaced upstream and downstream o2 sensors at same time replaced maf sensor both upper and lower intake plenums both value covers the idle air control valve the spark plugs all the spark plug wires and I still have check engin lite and system to lean code and when I step on breaks softly doing 60 the rpms Guage drops rapid from 1400 to 900 then bounces back to 1350 within seconds I have had this lean code for over a year and I stopped driving it until now fixing all this I checked there no leaks on vacume system or plenums mine is a federal emissions 2000 toyota 4runner millennium silver sport edition 4x4 3.4l v6
Old or new thread - stupidity needs correction
i believe you are sincere - so allow me to comment. A few of these posts are a bit misleading and border BS. The one saying that the 5VZFE doesnt like the full K&N CAI is such a case and point.
The MAF installed in the CAI measures the air so the ECM can set the injection up with the proper fuel. As long as you can supply enough fuel to get a perfect AFR - YOU ARE GOLD. The engine runs off of fuel & air, atomized, timed, and injected.
And since I run one of those same CAI's myself - (along with the supercharger, larger injectors, and the Walbro pump) - like the URD kit that many others bought from Gadget as well - common sense should kick in.
The only time the P0171 code will be able to become the PITA it is now, is when the air fed into the mix is UNMEASURED.
In other words IF the O2 sensor is good and reading true - the "extra" air is getting in by a leak.
Else the MAF would be measuring it correctly and the ECM would set the injectors to match that air with fuel.
Since it is NOT - it got in illegally. Vac leak. Gasket leak. Anywhere the motor can suck it in - is suspect. The O2 sensor can only be blamed if it is giving a false indication to the ECM.
Even the K&N thing about their filter oiling fouling MAFs was debunked years ago and their proof is on YouTube, if you care to see it.
Personally, I have run both the drop-in and full monty CAI rigs and prefer the later. I wish you the best at killing the code. But ask that you use your own common sense. Obviously yours is more real than others in this battle - including at least one Toyota service tech!!
i believe you are sincere - so allow me to comment. A few of these posts are a bit misleading and border BS. The one saying that the 5VZFE doesnt like the full K&N CAI is such a case and point.
The MAF installed in the CAI measures the air so the ECM can set the injection up with the proper fuel. As long as you can supply enough fuel to get a perfect AFR - YOU ARE GOLD. The engine runs off of fuel & air, atomized, timed, and injected.
And since I run one of those same CAI's myself - (along with the supercharger, larger injectors, and the Walbro pump) - like the URD kit that many others bought from Gadget as well - common sense should kick in.
The only time the P0171 code will be able to become the PITA it is now, is when the air fed into the mix is UNMEASURED.
In other words IF the O2 sensor is good and reading true - the "extra" air is getting in by a leak.
Else the MAF would be measuring it correctly and the ECM would set the injectors to match that air with fuel.
Since it is NOT - it got in illegally. Vac leak. Gasket leak. Anywhere the motor can suck it in - is suspect. The O2 sensor can only be blamed if it is giving a false indication to the ECM.
Even the K&N thing about their filter oiling fouling MAFs was debunked years ago and their proof is on YouTube, if you care to see it.
Personally, I have run both the drop-in and full monty CAI rigs and prefer the later. I wish you the best at killing the code. But ask that you use your own common sense. Obviously yours is more real than others in this battle - including at least one Toyota service tech!!
AntonioCm1983
New member
Totaly agree with you I'm running a cold air intake from volant for my 2000 4runner and have had it for years never once through any codes what so ever for the maf
superman786
New member
2000 4Runner SR5 w/ TRD SC
So I am currently having the P0171 code on a recently acquired 4Runner as well. It's a '00 SR5 with TRD Supercharger and 122K miles. Initially, I was getting the P0300 codes. Then with the help of my uncle we changed the valve cover gaskets (looked like it was leaking) and put new OEM spark plugs. That seemed to fix the P0300 codes I was getting, but now I have the P0171 code and it hasn't gone away for about a month. I tried the simple and cheap fixes already, cleaning MAF, replace PCV valve, and changing the air filter. My MPG is about 16 city and when I recently did a road trip, got as much as 18.5 MPG. So I am not seeing the huge MPG loss as others. Also, looking at the TRD SC manual, it actually mentions the P0171 in the troubleshooting table and has this to say:
So I am currently having the P0171 code on a recently acquired 4Runner as well. It's a '00 SR5 with TRD Supercharger and 122K miles. Initially, I was getting the P0300 codes. Then with the help of my uncle we changed the valve cover gaskets (looked like it was leaking) and put new OEM spark plugs. That seemed to fix the P0300 codes I was getting, but now I have the P0171 code and it hasn't gone away for about a month. I tried the simple and cheap fixes already, cleaning MAF, replace PCV valve, and changing the air filter. My MPG is about 16 city and when I recently did a road trip, got as much as 18.5 MPG. So I am not seeing the huge MPG loss as others. Also, looking at the TRD SC manual, it actually mentions the P0171 in the troubleshooting table and has this to say:
I tried to use the propane method to check for vacuum leaks and didn't notice any idle change. But I am not the most experienced working on cars, so not sure if my technique was correct. Two things I am currently suspecting is the manifold gasket since it was the only thing not changed when doing the valve cover gasket job. And the second would be the O2 sensor. I will do the manifold gasket first since it is much cheaper than an O2 sensor in California. I am also open to any suggestions because I am a novice to working on cars, but I do have a strong technical background.
AntonioCm1983
New member
02 sensors were the problem for me on my 00 4runner I also changed the plenum gaskets and manifold gaskets also did throttle body gasket and the p0171 went away for me after that
firemanj92
New member
I've got a Calif T4R with 270k miles and had a lean code that took me a month to chase down. All this came about after replaced the steering rack and rebuilting the front suspension since I had the rack out-completely unrelated to emissions codes.
It ended up being the front A/F sensor. Before we discovered it was a (new) bad sensor we changed out everything from the fuel pump, filter, vacuum regulator, injectors, spark plugs, coils (one tested bad), plenum gasket (twice felpro then back to OEM) and all vacuum lines, IAC valve, MAF, and both 02 sensors-still had a lean code. We then circled back to the front A/F sensor which the 1st one I bought was bad. I initially figured all those items were cheaper than the 02 sensors but in the end I had to buy them anyway. There isn't a sure way to test the sensors either only the heater circuit at home. CA emissions have an up-stream A/F sensor and a down-stream 02 sensor. Denso #234-9002 Front, Denso #234-4153 rear.
The 1st A/F sensor was the only thing I bought "new" thru ebay. It came in a non-descript box with no gasket so it was a little suspicious. I was trying to save a buck but ended up having to re-buy it thru AA with a coupon. I bought most the parts (all Denso/Toyo) from either AdvanceAuto since they have 20-30% off coupons or Amazon.
Good luck, I've got the other part #'s if you need them.
-J
Last edited:
Chief Hendog
New member
Hey I’m unable to make my own thread yet but I’m having the same problem. I have a 2002 4runner sr5. It threw this code so I hooked up a scanner and noticed my fuel trims at idle are high. I went through all the usual suspects so the only thing I can think of now is throttle body not fully closing. Does anyone know what percent open the throttle body should be at idle on the 2002. Mine is sitting at 14.1-14.5% but I thought it should only be like 7
AntonioCm1983
New member
Throttle blades should be open between 5 and 8 according to shop manuals i would also check the pcv as well as the fuel injectors some of them could be fouled
jgue467
Senior Member
0171? If fuel trims are all the way up, then its getting too much air.
Look for cracked hose intakes between MAF and metal intake runners.
Common to have the piece closest to the heat of the engine at metal runners crack over time. Here's a pic of what I replaced to resolve a 0171 on my runner.
Amazon.com: MOSTPLUS Air Intake Tube Cleaner Hose Replaces 1788262010 - Compatible with Toyota 4Runner 3.4L 1996 1997 1998 1999 2000: Automotive
Attachments
AntonioCm1983
New member
Thats another good point good idea cracked hose close to motor roge air
Andrewb123
New member
Issue resolved?
Superman786, were you able to resolve this issue? If so, what ended up fixing it?
I have 2000 sr5 w/ TRD supercharger, CAI, and 182K miles. Soon after installing the CAI I started getting the P0171 code. I checked for vacuum leaks using propane, verified all the vacuum lines were connected correctly, and cleaned the MAF. I’m near the point of reinstalling the stock airbox and filter since I need to get rid of the P0171 code to get my 4Runner through emissions testing.
I just ordered a new MAF, but I’m trying to avoid the rabbit hole of changing the MAF, 02 sensors, and all the gaskets.
Superman786, were you able to resolve this issue? If so, what ended up fixing it?
I have 2000 sr5 w/ TRD supercharger, CAI, and 182K miles. Soon after installing the CAI I started getting the P0171 code. I checked for vacuum leaks using propane, verified all the vacuum lines were connected correctly, and cleaned the MAF. I’m near the point of reinstalling the stock airbox and filter since I need to get rid of the P0171 code to get my 4Runner through emissions testing.
I just ordered a new MAF, but I’m trying to avoid the rabbit hole of changing the MAF, 02 sensors, and all the gaskets.
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