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Toyotapro, ASE master tech
Category: Toyota
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Experience:  ASE Certified, 10+ years Lexus and Toyota Certified
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2000 Toyota Avalon with 175000 miles will not ...

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2000 Toyota Avalon with 175000 miles will not accelerate when gas pedal is fully depressed. Was showing code P0171 before I erased it. Have put new fuel filter and air filter. Checked Alternator output. What next.


What you are describing sounds like you have a plugged catalytic converter causing an exhaust restriction. If the car won't accelerate and the RPM dont spike when the pedal is fully depressed, that is surely your problem. If it is that bad you should be able to feel the exhaust coming out of the tailpipe (or lack of it). The cat can also be temperature tested with a mechanics temp gun-it should be 100 degrees hotter at the exit than the inlet. Also manifold vacuum can be tested-if it drops under engine acceleration then it is an indication of restricted exhaust.

Let me know what you find out, I'll be glad to assist more if you need it.

Thanks for using JA
Ms Wrench

While Ms. Wrench has a good suggestion this is very unlikely on your car. Clogged converters almost NEVER occur on this car unless you ran it for a very long time with a misfire, you would also have a P0420 if this was the case. P0171 is 99.9% of the time a defective Mass air flow sensor on this car unless other codes are present also. The mass air flow sensor has a tendancy to do exactly as you say, does ok under normal loads but when you floor it the engine retard and almost seems to die-let off the gas a little and t spring back to life. I do recommend you also check the Throttle position sensor with a scan tool to make sure the on/off readings operate normally, this works in sync. with the MAF sensor but most likely this is a simple mass air flow sensor issue. Very simple repair a kid could do- 2 #2 phillips screws and an electrical connector. Part # XXXXX lists for $153.76



Customer: replied 9 years ago.
Reply to Peter's Post: I took the MAF off and looked and cleaned it. Should I just go buy another one or wait until I drive it a little and see what codes it shows. It will show something as the check engine light has been off and on for a long time. I just cleared the codes by accident. It usually comes back on after 50 or so miles of driving. There were three codes up before.
The vehicle has to have a severe lean condition/misfire or complete some drive cycle patterns before it will set a code again. Some customers have cleaned the MAF out with contact cleaner and had some success but this is a 50/50 chance. If the car still shows lack of power and will not hold wide open throttle then replace the sensor.
Toyotapro, ASE master tech
Category: Toyota
Satisfied Customers: 9974
Experience: ASE Certified, 10+ years Lexus and Toyota Certified
Toyotapro and 2 other Toyota Specialists are ready to help you
Customer: replied 9 years ago.
I drove 55 miles and check engine light came back on. Codes P0171,P0171,P0420. With both codes showing, would you suggest buying the MAS first and then see if I need a second CAT (first one at 80,000 miles furnished by Toyota). I have a bottle of Techron. Should I run it now or wait until problem gets solved?
P0171 is system lean, replace mass air flow. The p0420 you never mentioned before, do not drive the vehicle any more until you replace the sensor. You may have damaged or are currently damaging the catalytic converter due to lean issue. Replace the sensor and then check to see if code p0420 comes back.
Customer: replied 9 years ago.
Thanks for info. I just called and they have one in stock. I will go pick it up now. Sorry about the 0420 code. I forgot it when I erased it.
That's ok, let me know if I can be of further assistance. I assume you are buying the sensor from toyota to be sure you get the correct part and avoid duplicate concerns. Good luck with the repair and you know who to ask if you have further problems.
Customer: replied 9 years ago.
Just put in new MAS. Runs great. Thanks for the help. I will recomend you and talk to you when something comes up. Reset codes, will let you know if they show up again.

Thanks again
Customer: replied 9 years ago.
Reply to Peter's Post: I puchased from Auto Zone because we have no Toyota Dealer close by. It is a Toyota part,(it has the same everthing as the part that come off) just remanufactored. It runs great. I cleared codes. Will let you know if any come back. I have about 90 miles to drive tomorrow.

Thanks Peter
That was a lot better than driving 50 miles to dealer and paying him God knows what to fix it. I really don't trust shops to do you right. I carried my Father-in-laws car to GM dealer and he wanted 900 for anew AC compressor. I put in two cans fo 134 and it works just fine. That just makes me wonder if they have a clue. Not many places that have good people like you.

Thanks again

Thank you for your compliments, I will be here if you ever need me in the future. have a good evening and thank you again.
Customer: replied 9 years ago.
Drove 50 miles then came codes P0420, P0440. Then drove 50 miles back home Running from 55 to 75 MPH and it showed 29 MPG. Thats about the best it has ever done. Drove 35 miles of the 50 at 75 MPH.   Average MPH 60. What would you think now. I'm not going to put alot into this car. She runs good and gets 29 MPG, I'll probably just drive her.


P0440-evap leak, you most likely left the gas cap loose or pulled the evap line loose on the air box when you replaced the MAF sensor.

P0420, as I stated earlier, converters don't just fail normally on this car, most likely you damaged the converter by driving it with the p0171 code, converter is now defective.