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High rpm on neutral but flatting the gas pedal on D doesn't increase the rpm

Motor Vehicle Maintenance & Repair Asked by AdoobII on January 31, 2021

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.

2 Answers

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

Answered by Ike on January 31, 2021

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.

Answered by AdoobII on January 31, 2021

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