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I am making this question as an update to my previous question .

I am not sure if updating that question will draw attention to it or keep it buried in the sea of questions here, if it gets updated please merge the questions since this is an update but a one that brings a lot of questions.

Since I asked the last question and got no leads I bought a bluedriver OBD-II scan tool which brought up 5 trouble codes and a questionable live data values.

My car is a Lexus es300 made in 2002

This is a screenshot of the codes I got

As you can see, all the codes refer to a problem regarding one of the two A/F sensors in banks 1&2. using the live data feature and monitoring the long and short term fuel trim %, The long-term % at bank 1 was around -7.0% to -0.8% and at bank 2 the long-term % was higher at -7.8% to 4.7%. The short-term values are shown in the picture below. I am not sure if those values are good or not but I read somewhere that up tp 15% is normal but probably that's when the vehicle is moving?.

This is a screenshot of the live data values

Now moving into the Mass Air Flow rate, it ranged from 0.46 g/s - 95.04 g/s , the lower value is when the vehicle was idle and the higher value being when the vehicle is idle at +7k rpm. My car is a Lexus es300 made in 2002 and it's rated for 210 bhp, and the car's MAF averages at 66 g/s at 7k rpm. I assume that my car should have a MAF of at least 160 g/s, maybe 140 g/s because it's old, But maxing at 95 g/s is a problem. the max value specified in the range above happened because of the sudden change in the rpm or so I assume. the MAF rate averages around 66 g/s.

Here you can see that the Lambda values for both banks is around 1.000 so nothing is bad in the ratio.

Now I suspect that this is an airflow problem because all this fiasco started happening around the time when I changed the air filter, I have cleaned the MAF sensor by scraping the dust and using brakes cleaner and let it dry for a while before taking those measurements, I know brakes cleaner isn't the best option but it works and the MAF sensor was very clean when I saw it although I didn't change it before. And cleaning the sensor didn't change anything apparently.

Now my question is, could all the Air fuel ratio sensor trouble codes be popping up because of a problem regarding the air flow into the engine? in the top rated solutions part of the report, the bluedriver scan tool suggests changing the A/F ratio sensor, but one of the top solutions for all the codes changing the MAF sensor is a top rated solution as well even the knock sensor had changing the MAF as one of the solutions. Could all of these problems be caused by a faulty airflow? the car has almost no power and I have to rev up the engine to 3.5k+ rpm to be able to drive at 100 km/h (60 mph) whereas before this problem driving at 120 km/h was requiring an rpm of 2.1k.

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  • Did you repair / address all the faults and servicing items you mentioned in your original post. Air pipe & timing belt...
    – Solar Mike
    Aug 5, 2018 at 16:23
  • @SolarMike , yeah I changed the air pipe right after and the timing belt was changed aswell
    – AdoobII
    Aug 5, 2018 at 16:25
  • Did you clear the codes after fixing the intake tube? What’s engine vacuum? What kind of voltages are you seeing from the afr sensors?
    – Ben
    Aug 6, 2018 at 1:57
  • @Ben Hi Ben, the voltages are pretty normal I think, constant 3.2 - 3.3 volts. I didn't clear the codes but the problem should be fixed regardless of the codes existing or not as far as I know. tried it yesterday and when the car temperature rises to its normal level it starts to stop responding. the car behaves normally until the temperature reaches the normal level.
    – AdoobII
    Aug 6, 2018 at 15:57
  • @Ben Hi Ben, sorry I meant by my past comment the voltage reading that the OBD-II scan tool provides. which is the voltage of both O2 sensors which is 3.2 - 3.3 volts. as for the A/F ratio voltages I assume you mean the resistance between the two black wires? I don't have any means to measure a resistance or a voltage atm, gonna buy a multimeter soon and test that.
    – AdoobII
    Aug 6, 2018 at 16:06

2 Answers 2

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I thought I would update this thread with the solution to the problem so others find it useful in the future.

As others in the comments have suggested, I've tested the MAF sensor but it wasn't faulty. I was desperate so I cleared all the codes and ran the car for a while (driving the car after clearing the codes was normal and without the rpm and power problems) looking for new error codes. The error that came back was the knock sensor error message. I've bought 2 from eBay and replaced both my knock sensors.

The problems with my car arose from the fact that my car would go into something called "limp mode" which would decrease the engine's power as to not damage it or the car because of some error detected by the car's computer.

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Id try maf sensor. My maima was basically doing the same bfore i replace my maf.

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    Welcome to Motor Vehicle Maintenance & Repair! Could you elaborate as to why it could be the MAF? Also include how one would go about checking the MAF. We try not to promote Remove & Replace mechanics here on this site, as it usually just costs more money and fixes absolutely nothing. A good answer will include diagnostic methods used to fix an issue as well as the reasons why it might be the cause in the first place. Guessing is just guessing, which is not a good thing.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 6, 2018 at 12:20
  • Hi Ike, I have already stated that I cleaned the MAF sensor in my question above :D. I suspect the problem involves an air intake problem but I want someone to confirm it. the max Mass airflow sensor reading is 90 g/s and I think it's the problem. I just want someone to confirm it. I am going to replace my A/F sensors and the two O2 sensors all together and see if the problem gets fixed since those sensors are very old anyway.
    – AdoobII
    Aug 6, 2018 at 16:01

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