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Dan, ASE Certified Technician
Category: Lexus
Satisfied Customers: 1668
Experience:  Auto Technician
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I own a 2007 Lexus RX400H with 157,000 miles on it. The car

Customer Question

I own a 2007 Lexus RX400H with 157,000 miles on it. The car has ran perfect for me up until my radiator blew a few months ago. I got the radiator replaced along with the fan motor. After the radiator and fan were replaced the car ran good for two hours and then it started misfiring and it threw a code that was for multiple random misfires. I then took the car to my Lexus dealer and they thought that the car had bad gas but they tested the gas and that was not the problem. The Lexus dealer then hooked the car up to their code reader and they got the same reading on the codes as being multiple misfires. The Lexus dealer's diagnosis was that the car needed to have the spark plugs, the ignition coils and the fuel injectors replaced and that would then fix the problem. I proceeded first with having only the spark plugs and ignition coils changed and held out on the changing the fuel injectors. The problem with the car misfiring stopped for one month and then it started misfiring again. I then proceeded with changing the fuel injectors and the problem still persists. When I am driving the car, the misfire is very noticeable until I fully get on the gas pedal and then the misfire will go away. I looked all over the internet in hopes of figuring out what is wrong with my car and I read that if I spray carb cleaner into the engine intake and if the misfire then goes away then that would mean that I have a vacuum leak. So I sprayed the carb cleaner into the engine intake and the misfire goes away and the car will work fine for about 4-5 min. and then the misfire comes back. I think that it could be a vacuum leak but at this point I don't want to keep throwing money into the car and that not be what will fix my problem. All I know is that the problem with the misfire on my car started after my radiator blew up and it had never done this until that happened. I have not been able to drive my car now for almost a month and I am in dire need of finding a resolution to my problem. Listed below is the last OBD II reading that was done on my car on 10/15/2016. I don't want any guesses or what you think it might be because I know that the code my car threw for multiple misfires could mean a range of things, however, I have eliminated several factors for you already and I hope an experienced mechanic can give me an answer. Thanks, ***** *****
OBD II Reading as of 10/15/2016:
DTC present : p0300
Freeze frame data
> Freeze frame report generated by Torque for Android
> Vehicle VIN: Not present
> Vehicle Manufacturer: Unknown
> Vehicle Calibration ID: 348A0100
> Freeze frame information:
> ------------------
> Fuel Status = 0 byte
> Engine Load = 91.373 %
> Engine Coolant Temperature = 158 °F
> Fuel Trim Bank 1 Short Term = -4.688 %
> Fuel Trim Bank 1 Long Term = 6.25 %
> Fuel Trim Bank 2 Short Term = -2.344 %
> Fuel Trim Bank 2 Long Term = 7.031 %
> Engine RPM = 2,033.5 rpm
> Speed (OBD) = 32.933 mph
> Timing Advance = 25 °
> Intake Air Temperature = 87.8 °F
> Mass Air Flow Rate = 44.84 g/s
> Throttle Position(Manifold) = 35.294 %
> Run time since engine start = 25 s
> O2 Sensor1 Equivalence Ratio = 0.991
> O2 Sensor5 Equivalence Ratio = 1
> Distance travelled since codes cleared = 0 miles
> Barometric pressure (from vehicle) = 14.069 psi
> Catalyst Temperature (Bank 1,Sensor 1) = 771.26 °F
> Catalyst Temperature (Bank 2,Sensor 1) = 771.26 °F
> Catalyst Temperature (Bank 1,Sensor 2) = 219.02 °F
> Catalyst Temperature (Bank 2,Sensor 2) = 219.02 °F
> Voltage (Control Module) = 13.613 V
> Engine Load(Absolute) = 67.451 %
> Commanded Equivalence Ratio(lambda) = 0.997
> Relative Throttle Position = 17.647 %
> Ambient air temp = 78.8 °F
> Absolute Throttle Position B = 71.765 %
> End of report.
Submitted: 9 months ago.
Category: Lexus
Expert:  Dan replied 9 months ago.

Hello my name is***** am an ASE Master Technician and I am glad to help you with your question.

Expert:  Dan replied 9 months ago.

This does sound like a vacuum leak, it you spray the intake and the rpm changes that indicates a vacuum leak. I would replace the intake gaskets and check all hoses for cracks. Positive long term fuel trims indicate a vacuum leak.

Another way to check for vacuum leaks is with a evap smoke machine. You fill the intake up with smoke and can see the leak.

You mass air flow reading seems high at 2k rpm. I would try removing the MAF and using some MAF cleaner to spray the electrode it may be dirty and causing your problem.

Expert:  Dan replied 9 months ago.

Please reply to this if you need more help and we can continue this conversation at no extra charge. This does not have to be my only answer. If you are satisfied with my service, please rate at the top of the screen. Rating does not close out your question. Remember, sometimes it is difficult to completely diagnose your vehicle without being there, but I will try to give you the best answer I can. Hoping to be giving you 5 star service.


Customer: replied 8 months ago.
Hello Dan, I am very sorry I didnt read your email but the email got put into my junk mail. I found it today because I was going to call Just Answer and find out why I hadnt received an answer. My mechaic did remove the plenum and fully checked the gasket for any imperfections, cracks or causes for concern but said that it looked good. All hoses were checked and all were good. Would you still recommend replacing gasket? He has not removed the Mass Airflow and cleaned as you said. He is coming over today and I am having him do that immediately.
Expert:  Dan replied 8 months ago.

Were you able to correct the problem?

Expert:  Dan replied 8 months ago.

Hello again Dan here,

I am contacting you because the post has not been closed or rated.

This question is coming up on 7 days which means it will time out and close.

You have already paid to get this question answered, but you have not rated.

Let me help some more. Is there anything else I can help you with?

If I did not give you 5 star service, please let me know what I missed.


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