How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Toyota Service Your Own Question
Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
Satisfied Customers: 4945
Experience:  30 + years of experience; Multiple Award Winning Svc Mgr; Just Answer Customer's Choice Award Winner
14892859
Type Your Lexus Question Here...
Toyota Service is online now
A new question is answered every 9 seconds

I have a 1998 lexus es300 with a ongoing po171 dtc JA: Thanks.

Customer Question

I have a 1998 lexus es300 with a ongoing po171 dtc
JA: Thanks. Can you give me any more details about your issue?
Customer: it will run rough studders occasionaly
JA: OK got it. Last thing — Lexus Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: Lexus
Expert:  Toyota Service replied 1 year ago.
Hello. Welcome to Just Answer. Please allow me to assist you. Have you done anything with regard to the P0171 Mass Air Flow Sensor code? Please advise.
Customer: replied 1 year ago.
I committed to 5 deposit and 15 final
Customer: replied 1 year ago.
Yes new 02 sensor new mass air flow sensor new rear exhaust manifold
Expert:  Toyota Service replied 1 year ago.
Ok. The P0171 code is fairly common. We see it a lot, especially with cars with dirty air filters, incorrect (non-Lexus) air filters, or, worst yet, K & N air filter cartridge panels. The P0171 basically indicates that the engine is not seeing proper air flow entering the engine (ie a too "lean" condition, or, too much air.... If you have replaced the Mass Air Flow sensor with a genuine Lexus part, I would be looking for vacuum leaks at the intake manifold. If you do not find any loose or cracked, or poor fitting vacuum hoses, I would recommend replacement of the intake manifold gasket. The 171 air flow code is common to Non-Lexus Mass Air flow sensors, too.
Expert:  Toyota Service replied 1 year ago.
Please confirm that you have received my input. If you have any questions, please feel free to ask. Thanks.
Customer: replied 1 year ago.
The engine was smoke tested that is how i found the cracked rear intake manifold. there was no evidence of a intake manifold leak
Expert:  Toyota Service replied 1 year ago.
Smoke tests are very unreliable, in my opinion. A p0171 is a too lean condition. This means air is getting into the engine that is not being measured by the Mass Air Flow sensor. Either the MAF is faulty or non-Lexus, or you have a vacuum leak. This will also cause a stumble.
Customer: replied 1 year ago.
I have had it 3 separate qualified mechanics all was inspected by them . hence the new mass and new 02
Expert:  Toyota Service replied 1 year ago.
I fond it odd that they would recommend (and install) a new O2 sensor with no O2 sensor code. If any sensor was to be replaced, it should have been the Air-Fuel sensor, not the oxygen sensor, but only with a AF sensor code. With all due respect for your associates working on your car, there seems to be a bit of guessing on this issue.
Customer: replied 1 year ago.
that is why I am on this site looking for an expert
Customer: replied 1 year ago.
Are you still there?
Expert:  Toyota Service replied 1 year ago.
If this car was in my shop. the first thing I would be doing would be looking at the spark plugs, not exhaust manifolds. If this car has anything but Nippondenso spark plugs installed, get the non-Nippondenso plugs out of there and get the correct spark plugs installed. Next, get the right/factory air filter for the car. Throw away the K & N filter if you have one).
Expert:  Toyota Service replied 1 year ago.
Then clear the code, and add a can of a really good fuel injector cleaner (we recommend BG 44-K). Put the cleaner in the tank and top off the tank to 3/4 full. Drive the car and run the fuel out as fast as possible (the cleaner loses strength if it sits). The retest for the P0171 code.
Customer: replied 1 year ago.
The plugs and air filter was replace at my local toyota dealer
Wouldn't a bad plug cause a miss fire code
Expert:  Toyota Service replied 1 year ago.
Not necessarily.
Expert:  Toyota Service replied 1 year ago.
Then get the BG 44-k and run it thru the fuel system, and look for vacuum leaks. This is most likely a small leak at the intake manifold.
Customer: replied 1 year ago.
I will try that and get back to you
Expert:  Toyota Service replied 1 year ago.
ok
Customer: replied 1 year ago.
I also have an engine analyzer that has live data record. anything I should look for
Expert:  Toyota Service replied 1 year ago.
Pattern A/F Sensor Voltage value Short−Term Fuel Trim1: 2.8 V (* 0.56 V) or less Changes at about − 20 %2: 3.8 V (* 0.76 V) or more Changes at about + 20 %
Customer: replied 1 year ago.
Thanks I will check and get back with you
Expert:  Toyota Service replied 1 year ago.
ok