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Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
Satisfied Customers: 4674
Experience:  30 + years of experience; Multiple Award Winning Svc Mgr; Just Answer Customer's Choice Award Winner
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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: 11 months ago.
Category: Lexus
Expert:  Toyota Service replied 11 months 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 11 months ago.
I committed to 5 deposit and 15 final
Customer: replied 11 months ago.
Yes new 02 sensor new mass air flow sensor new rear exhaust manifold
Expert:  Toyota Service replied 11 months 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 11 months ago.
Please confirm that you have received my input. If you have any questions, please feel free to ask. Thanks.
Customer: replied 11 months 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 11 months 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 11 months 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 11 months 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 11 months ago.
that is why I am on this site looking for an expert
Customer: replied 11 months ago.
Are you still there?
Expert:  Toyota Service replied 11 months 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 11 months 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 11 months 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 11 months ago.
Not necessarily.
Expert:  Toyota Service replied 11 months 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 11 months ago.
I will try that and get back to you
Expert:  Toyota Service replied 11 months ago.
ok
Customer: replied 11 months ago.
I also have an engine analyzer that has live data record. anything I should look for
Expert:  Toyota Service replied 11 months 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 11 months ago.
Thanks I will check and get back with you
Expert:  Toyota Service replied 11 months ago.
ok