PO171 help please

[TucsonMike]

Hi,
On way home from Flagstaff to Tucson going up a large hill the chech engine light came on. I didn't have my code reader and car was running fine, so I wasn't concerned. Once I got home read the PO171 code I have done a lot of research on this code, I check for obvious vacuum leaks and also I put in a genuine Toyota MAF to see if that would change my STFT and LTFT, which it really didn't. Note: my new MAF I got off ebay several years ago, so could be fake. This is where I could uses some advice. My STFT are low 0 to 10 and the LTFT are maybe a tittle higher at idle. When I increase the RPM I see the LTFT increase up to 20 to 25 percent, the STFT fuctuates in 0 to 10 at higher RPM , from which I read is more of a fuel issue or other and not vacuum leak. Is that correct? My readings for O2 sensor bank one respond rapidly from .05 to .9 volts. Fuel pump and fuel filter was replaced within a year ago. Car drives fine. I have a 2000 with v6 and 5 speed. Federal emission, 300k. Last time I changed 02 sensors was 160k, but they seem to respond well to RPM changes. Appreciate it if anyone has experience seeing the LTFT increase with RPM with this of issue and can provide input. Thanks MikeM

 

[TucsonMike]

I should add that I clean the TB about 50k mules ago and the rubber tube connecting to the TB is showing some cracks. I had replaced that before and will replace it again. I will also look at TB today to see how clean it is

Thanks

MikeM

 

[mtbtim]

If you got the MAF off Ebay, it's most likely fake, especially if the price is WAY under OEM cost. Try cleaning the contacts first. If that doesn't work, get yourself an OEM MAF and your problem will most likely go away.

 

[TucsonMike]

Thanks Tim for the reply. I drove the vehicle around a lot more today and my fuel trims r better, like in the 8 to 10 range for LTFT and check engine light didn't come back on. Im going to continue to monitor it and see how it does. My son has a 3rd gen as well, so Im going to look at his fuel trims for comparison, kaybe even use his MAF. I do plan on cleaning my old one and putng it back in to see if anything has changed.

Thanks
MikeM

 

[jgue467]

So did the 0171 stay away after clearing it?

If not, I'd suspect a very fine crack in the air hose between maf and plenum.

I'd only clean an original maf, with the proper cleaning solution and No Touching whatsoever with anything.

Bend the air hose at the cracks, they will be very slight and tough to see yet after 20+ yrs we know they're there under all that heat they take, go OEM and you'll be set to go for along time.

Here's the part for an '01, Luck.

 

[TucsonMike]

After I cleared the code and put new MAF it has not come on in over 50miles of driving. I did order new OEM hose and will replace that in near future and clean my old MAF and perhaps put it back in as well just to see if it is any different.

Thanks for replies. Appreciate the help

MikeM

 

[spartacus]

Hi,
On way home from Flagstaff to Tucson going up a large hill the chech engine light came on. I didn't have my code reader and car was running fine, so I wasn't concerned. Once I got home read the PO171 code I have done a lot of research on this code, I check for obvious vacuum leaks and also I put in a genuine Toyota MAF to see if that would change my STFT and LTFT, which it really didn't. Note: my new MAF I got off ebay several years ago, so could be fake. This is where I could uses some advice. My STFT are low 0 to 10 and the LTFT are maybe a tittle higher at idle. When I increase the RPM I see the LTFT increase up to 20 to 25 percent, the STFT fuctuates in 0 to 10 at higher RPM , from which I read is more of a fuel issue or other and not vacuum leak. Is that correct? My readings for O2 sensor bank one respond rapidly from .05 to .9 volts. Fuel pump and fuel filter was replaced within a year ago. Car drives fine. I have a 2000 with v6 and 5 speed. Federal emission, 300k. Last time I changed 02 sensors was 160k, but they seem to respond well to RPM changes. Appreciate it if anyone has experience seeing the LTFT increase with RPM with this of issue and can provide input. Thanks MikeM

-10 To 10 STFT is normal. long term 20 to 25 under load is high. The maf reading at idle 700 rpms +/- a 5 or10, should be 4.65 Hg .If it's low or hi then your maf could be the issue. Replace it with a Denso 197-6020.

 

[gamefreakgc]

Lean code triggers above +30% fuel trims. Most code readers max out at 30% but I had one record up to +39.5% and then it threw a P0171 code (I was MAF tuning). I think you found your issue. Continue to replace any hoses that are cracked as they may 'look fine' but once it gets hot in the engine bay and the rubber gets softer it's not fine anymore.

 

[TucsonMike]

I hope I found issue. Yes, will replace cracked hoses.

Thanks

MikeM