ROOFGOOF

I searched but didn't see anyone with this code with the same issue I am having.

Hooked up the code machine and found it showing PO171 bank 1 (too lean) code. Its been on awhile and I've noticed that when at full open throttle my rig seems to bog down and hesitate (no power). I have to back off the throttle 1/2 way and then the motor picks back up like it should.

I am currently getting 17 mpg. Due to the hesitation, what could this be from? O2 sensor? MAF? ,etc.......
My rig is a 1999 4Runner Limited 3.4L.

THanks!!!
Tim

fillsrunner4

Could be: Lots of possabilities

Air induction system

Injector blockage

Mass air flow meter

Engine coolant temp. sensor

Fuel pressure

Gas leakage in exhaust system

Open or short in A/F sensor (bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

PCV valve and hose

PCV hose connection

EFI main relay

A/F sensor heater and relay circuit

Read this link it might help you track the cuplrite
Diagnostic codes

toytech76

More than likely its your MAF. Clean or replace it and you will be good

ROOFGOOF

I just cleaned the MAF....it was alittle gunky and I wiped it clean with a q-tip. I put everything back together and now the truck is hesitating even worse! I reset the battery cables after I cleaned the MAF and now my engine light is NOT lit.

However, I threw back on the code reader and there is the following little icons blinking.
Catalyst Monitor
Evaporative system monitor
O2 sensor monitor
O2 sensor heater monitor.

Its not reading the PO171 code now...probally because I reset the battery cables by touching them together.

TC4RNR

i've played with a rental code reader from Autozone recently, these monitor data you mentioned need more time to complete. hint you said you unplugged the battery cable, you need to drive few hundred miles to get these tasks completed.

toytech76

Whatever you do..you do NOT want to touch any of the wires of your MAF with anything. Clean it with MAF cleaner or brake kleen and some compressed air and thats it. You will probably need to replace it now

ROOFGOOF

Well I sprayed some brake kleen on it and put it back in... my truck is running better again. But I still have the hesitation at highways speeds. When traveling and I open the throttle, I get alot of hesitation. If I leave off of the pedal about 1/2 way the motor kicks back in and runs fine.

My check engine light came back on, so it looks like I am back to where I was in the beginning. I am going to see if its throwing the same code.

Fink

Check and make sure it's the same code...odds are it will be. 99% of the time its the MAF.

Using the q-tip on it may have messed it up...those wires are extremely sensitive. The slightest change in position can alter it's readings and mess it up.

Here is a similar thread as well as this one. Looks like the MAF was the culprit in these two.

That code sounds eerily familiar...it may have been thrown back when I was fighting with the God forsaken Cali spec emission issue I had with my '99. I had a bad/clogged cat and a bad O2.

Fink

ROOFGOOF

Well, I just rechecked it and its still throwing the PO171. I don't think the q-tip messed anything up with the MAF, especially after I used brake cleaner on it. Its running back the way it use to before I messed around with the MAF.

The sensor is throwing the 171 code and flashing 2 icons.
- Evaporative system monitor
-O2 sensor monitor

??????????????

I guess I will replace the MAF.... I would hate to drop that $$$ if its not the culprit.

Fink

I will check with my contact at the dealership here locally and see if he can find out anything, don't go buy an MAF just yet.

Fink

ROOFGOOF

I just called. The tech on the phone said it sounds like a MAF issue.... 156.00 bones. In stock....

Let me know. Thanks!!!

toy_tek

You can test the MAF resisitance with an ohmmeter. I only have the FSM for the older model, maybe someone can post up the terminals and specs you're looking for.

Alternatively you could swap the MAF with someone else's truck - its pretty quick to do.

Since its happening at full throttle (per your initial post) I might look into your fuel system a little closer. Maybe your fuel filter is clogging up and can't supply needed fuel at full throttle.

Lastly - I just "fixed" my P0171 that has been on since January. I have two threads pertaining: Here and Here. But before your read those... It was a weak or dead battery cell. Nothing in the FSM addresses battery voltage for a P0171, so it was kind of a surprise to me. I noticed my starting was kinda slow and the battery was older so I changed it without any inkling that it might fix the CEL. A day or two later the CEL went out and hasn't been back.

Fink

Yup, definitely the MAF. $156 seems too high. I wouldn't pay more than $130.

Fink

duskie

I had been buying my parts from conicelli for years. They have great price, good service, & ship fast. I believe they have it for less than $120 + shipping.

Consider yourself lucky you don't have 96-98 4runner. It cost at least $500+ for new assembly.
For anyone has 96-98, think of $500+ before you decide to clean it with hard object.

98runner210

Just scrape the MAF filaments clean with a screwdriver lol. I thought I had a MAF issue at one point. I got a used one dirt cheap and have been hanging onto it after seeing the cost of a new one. If you do end up needing a new MAF for the 96-98 cross reference it. I can't remember but it was the same for i think some avalons, es300, and something else.

toytech76

yah, the price for a new one for a 96-98 is around $500. One of the reasons I converted my MAF to the 99-02 style

toy_tek

Ditto.

duskie

Wondering what does it take to convert from 96-98 to 99-02 MAF?
could I reused air-box, air-intake tube, & connector to MAF?

ROOFGOOF

111db, I have a newer battery so I don't believe its a voltage issue. My rig always fires right up.

duskie, thanks!!! I will look into that website. CHEERS!!!

None of my friends have a 3rd generation 4runner to swap the MAF out. Thats a good idea though! Looks like I need new friends

I think I am going to swap out my fuel filter too. Its still the original.

Thanks everyone for the advice!

toytech76

You need an airbox from a 99-02 taco or 4runner with the MAF. It will bolt right in and hook right up to your air tube. You will need to move the pins on the MAF connector tho. I got my used airbox from a wrecking yard for $50 without a MAF