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Tom
Tom, ASE Certified Technician
Category: Lexus
Satisfied Customers: 25927
Experience:  ASE Certified Master Technician qualified to work on all makes and models.
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1999 Lexus RX300: The check engine light..acceleration..knock sensor

Resolved Question:

I have a 1999 Lexus RX300. The check engine light has come on & the gas mileage is horrible almost doubling our weekly gas ups, delays in acceleration 1 to 2 times a day. Took it to mechanic & they said computer indicates I need a ox sensor bank 1 & knock sensor bank 2. End up replacing those sensors & getting a fuel injection cleaning & tune up. The check engine light came back & the car is running crappy again. Need help quick!
Submitted: 5 years ago.
Category: Lexus
Expert:  lexpert replied 5 years ago.
Hello and thank you for using just answer! To properly help you here I need a complete list of active code #'s please.
Customer: replied 5 years ago.
Code PO 171 - Bank 1 system too lean
Code PO 330 - Knock sensor sensor two
Transmission Fluid full and looks clean smells burnt

Forgot to mention the rpms revs up to a 3 or 4 @ 50 to 60MPH & doesnt seem to want to change gears
Expert:  lexpert replied 5 years ago.
Did they replace both knock sensors and the sub harness or just one of the knock sensors?
Customer: replied 5 years ago.
Just one - bank 2. whats a sub harness?
Customer: replied 5 years ago.
Relist: Answer came too late.
Expert:  Tom replied 5 years ago.
Didi you still need help?
Customer: replied 5 years ago.
Yes.
Expert:  Tom replied 5 years ago.
The problem is the sub harnesses to the knock sensors need to be replied . The p0171 code is from a faulty mass are flow sensor and this would need to be replaced to fix these issues . Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.
What all does this entail? How much? How long of a job is this?
Expert:  Tom replied 5 years ago.
The knock sensor sub harness is pretty involved the intake needs to come off about 3 hours so 300 parts and labor. The mass air flow sensor about 10 minutes labor and part about 250. These are the next steps. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.

How will this help with the high reving rpms when driving at higher speeds?
Expert:  Tom replied 5 years ago.
The mass air flow sensor itself is bad and there can be a leak in the air tube going to the mass air flow sensor and that will cause this so start there next. Also the knock sensor harnesses when damaged affects the signal to the ECM for the proper timing and transmission shift points . These are what need to be checked next . Hoped this helped . Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.

Is there anyway to check if the knock sensor harness is damaged or not?
Expert:  Tom replied 5 years ago.
If you still have the P0330 code you need to remove the intake to check it regardless . Hoped this helped. Positive feedback and bonuses greatly appreciated.'
Customer: replied 5 years ago.

How do you check to see if the mass air flow sensor is bad?

Expert:  Tom replied 5 years ago.
Here's how to clean it.
ClickHere
If it helps a little bit it's shorted out and needs to be replaced. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.

How do you check if its shorted out?
Expert:  Tom replied 5 years ago.
There will be no resistance or very little. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.


Im sorry im not a mechanic, can you more thoroughly explain what you mean when you say "No resistance or very little? I just need a way to check to see if my mass air flow sensor is faulty or not.
Customer: replied 5 years ago.
Relist: Answer quality.
Expert:  Tom replied 5 years ago.
This will help.
ClickHere
Hoped this helped. Positive feedback and bonuses greatly appreciated.
Tom, ASE Certified Technician
Category: Lexus
Satisfied Customers: 25927
Experience: ASE Certified Master Technician qualified to work on all makes and models.
Tom and 2 other Lexus Specialists are ready to help you
Expert:  Tom replied 5 years ago.
Did you need anything else ? Don't forget to click the green accept button so I get credit for all my help.
Customer: replied 5 years ago.
Relist: Answer quality.
Expert:  Tom replied 5 years ago.
I spent alot of time with you on this. If his was a shop it would have cost you 200 dollars plus to trouble shoot your vehicle . What I told you is what's wrong and this is what needs to be checked and fixed. I've been in the field over 20 years have over 17,000 satisfied customers site wide who I have saved thousands of dollars for. My answer quality is perfect . If you never intended to accept the answers giving for the correct diagnosis you should have never continued. I work very hard to help people and this is not how experts should be treated here. My answers are correct and direct . If you don't want to pay for a correct diagnosis that just saved you undress of dollars that's your choice . Best of luck to you. This will be forwarded to customer service so this does not happen to another expert.
Customer: replied 5 years ago.

First of all you are coming across very pushy & thats not professional! Besides all of your typos your answers were not clear enough & I was pushing for clarity which is my right as a customer! I suggest if you don't have the patience to answer questions from your more thorough customers you should pass the job on to an expert that does. I will accept the answer given but you can guarantee a thumbs down on your review! "Patience is a virtue"

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