MTL_4runner

The ECU may turn the CEL on or off depending on the conditions seen, but I wouldn't count on it staying off.

04 Rocko Taco

Agreed. You should at least get your contingecy plans in place and source some parts for when it comes back on, because it probably will.

Potomacduck

Don't spend too much time trying to diagnose a bad MAF sensor. I learned the hard way. I had a bad sensor which was running the mixture way too rich. I tried cleaning it, ignoring it, etc.

The bad fuel/air mixture tanked my catalytic converters. I'm embarassed to tell you what that cost me. MAF's are cheap by comparison!

ebelen1

Update: 9/25/06

Again, yotatech comes up w/ the right answer. I changed my MAF (thanks to Evan at Northridge Toyota for a great deal) last week and no CEL. I didn't want to post until I had a week code-free.

I did change my A/F sensor first, which may not have been the reason for the code but at 100k miles, I figured I'd need a new one sooner or later.

MTL_4runner

Good to hear Edwin, I think you made a wise decision to change the A/F sensor anyway. If you want to get optimal gas mileage, that sensor needs to be working 100% when giving feedback to the ECU. Glad you got it solved.

ebelen1

Only thing Jaime is I'm not getting mpg w/ both a new A/F sensor and MAF sensor. I wish I was...

Stevo3

I just replaced my MAF, no luck getting rid of the code. But, what is this A/F sensor? i thought it was the MAF sensor. I guess im wrong, Sorry for being an idiot.

MTL_4runner

In most cases the P0171 indicates a bad MAF sensor (sometimes they can be cleaned, sometimes they need to be replaced as it did in Edwin's case). The other possibility for the code is likely the A/F sensor (on trucks 99-02, the front O2 sensor was replaced by what is called an Air/Fuel sensor). There are a few places to get them cheaper if you do a search on YT (Evan - Northridge, Phil - strapp22 or URD).

Stevo3

Well then that is why i dont know about the A/F sensor. My rig is a 96 runner.
But that is my next step is to change the first O2 sensor. I just bought a new MAF and no luck with that, just a huge dent in my pocket . Maybe ill pick up an O2 sensor today, ofcoarse an OEM Denso. The NAPA by me carries them for $100, AutoZone/Checker for $130. And I seen Gadget has them for $80. Ill just get one now, instead of having to wait for shipping. Hehehe, Ill just milk the clock today for 1.5 hours. to make up for that $20.

ebelen1

Good luck. I just thought it was the A/F (O2) sensor as the mileage was showing that it may be needed. It's pretty rare as I've searched but I don't see many changing MAFs (unless they are s/c'd and want to get a Supra MAF).

Did you try to also search for vacuum leaks as this can cause the same code? I did check but didn't notice anything on mine.

MTL_4runner

On the 96-98's for whatever reason, the MAFs rarely go "bad" compared to the 99-02's......sorry this bit of advice comes a little too late to be of any help after you dropped a few C-notes on a new MAF. My bet is your front O2 sensor being the culprit.

Stevo3

Well, My truck is S/C'd, and didnt the light didnt come on for about 500 miles after it was put on. If any knows a reason for that. Ill try the O2 sensor as i said and see if that helps it. Thanks for the replies!

Stevo3

Well, After looking over the hoses on my truck, I did notice a Hissing noise comming from the S/C. All my hoses are correct and okay. But I have the GEN I S/C (the grey one). And the hissing is comming from the "thing" near the bypass vavle. I dont know what its called But its like a rectangled piece that fits into the intake part then turns into a cylinderish piece next to the bypass valve.....

Anyways I think this is the main culporate to my "Bank 1 Too Lean" code. As the truck gets up to temp, Its starts to run pretty rough (engine rocks back and forth). I then place my hand over the part thats leaking and it idles back to normal, which is smooth running. Is there anyone out there with they Grey S/C? I think Gadget has one but I would think he has upgraded to the newer one.

My Question is now, am I able to use the Hi Temp Gasket maker to put in the part that is sucking in extra air? Because I cannot find anything about a true Gasket for that area. Thanks for the help!

ebelen1

I think it's better you start a new thread w/ your question or it may get buried. There's a pretty active s/c group here that have been very helpful to those having issues...

MTL_4runner

I think AJatx just had almost the exact same issue you are having:
https://www.yotatech.com/forums/f2/p0171-trouble-root-causing-95672/

An auto parts store should have o-ring kits with what you need.