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Looks like it is the 2nd o2 sensor causing the issue. If you have taken the cats off did the o2 sensors get reinstalled? I have read there is often a trick with a different adaptor sometimes being used. Most seem to use the o2 simulators and block up the holes.
 

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2002 Lexus IS300
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If you have those codes after replacing the spark plugs and coil packs, I am unsure changing the MAF will affect anything. You still have issues on two cylinders. You have no fault code for a MAF. You also only have one code for the heater circuit for the downstream O2 on bank 2. That o2 should be replaced, but not because it isn’t functioning, the heating element inside of it has failed causing that code.

You either have a large vacuum leak somewhere related to bank 2. Or you have a faulty injector on one or both of those cylinders. Worse case would be bad compression in the cylinders that are misfiring.

If it was a MAF issue then ALL cylinders would suffer. Thé upstream o2 sensors provide the most viable fuel adjustments to the ECU and there are no codes showing for that.
 

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04 IS300 automatic
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Discussion Starter #23
Looks like it is the 2nd o2 sensor causing the issue. If you have taken the cats off did the o2 sensors get reinstalled? I have read there is often a trick with a different adaptor sometimes being used. Most seem to use the o2 simulators and block up the holes.
I am so bummed rn.?
So are you getting only ONE bank that’s running rich? If so I would monitor that upstream O2 sensor to see if it is stuck or “lazy.”

Also I would check short term fuel trims for that bank. You might have a faulty injector.
yes, I think it is injector..plus iv never used the sea foam the 30k miles iv driven the car.?Idk what fuel trim is lol I just started learning about exhaust/cats/headers O2gas mixture and how it all kinda works. This Dickwad that did the job made out good scrapping those cats and saying basically fuck you after he put the header on and it wasn’t running right. He told me nothing about needing To order O2 simulator etc.
 

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04 IS300 automatic
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20 Posts
Discussion Starter #24
I am so bummed rn.?

yes, I think it is injector..plus iv never used the sea foam the 30k miles iv driven the car.?Idk what fuel trim is lol I just started learning about exhaust/cats/headers O2gas mixture and how it all kinda works. This Dickwad that did the job made out good scrapping those cats and saying basically fuck you after he put the header on and it wasn’t running right. He told me nothing about needing To order O2 simulator etc.
He told me what to order which was a shitty header with a worthless gasket from eBay somewhere
I am so bummed rn.?

yes, I think it is injector..plus iv never used the sea foam the 30k miles iv driven the car.?Idk what fuel trim is lol I just started learning about exhaust/cats/headers O2gas mixture and how it all kinda works. This Dickwad that did the job made out good scrapping those cats and saying basically fuck you after he put the header on and it wasn’t running right. He told me nothing about needing To order O2 simulator etc.
 

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04 IS300 automatic
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20 Posts
Discussion Starter #25
Looks like it is the 2nd o2 sensor causing the issue. If you have taken the cats off did the o2 sensors get reinstalled? I have read there is often a trick with a different adaptor sometimes being used. Most seem to use the o2 simulators and block up the holes.
Yes they are all there and plugged in. Not with any adapter
 

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04 IS300 automatic
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Discussion Starter #26 (Edited)
If you have those codes after replacing the spark plugs and coil packs, I am unsure changing the MAF will affect anything. You still have issues on two cylinders. You have no fault code for a MAF. You also only have one code for the heater circuit for the downstream O2 on bank 2. That o2 should be replaced, but not because it isn’t functioning, the heating element inside of it has failed causing that code.

You either have a large vacuum leak somewhere related to bank 2. Or you have a faulty injector on one or both of those cylinders. Worse case would be bad compression in the cylinders that are misfiring.

If it was a MAF issue then ALL cylinders would suffer. Thé upstream o2 sensors provide the most viable fuel adjustments to the ECU and there are no codes showing for that.
They did a compression test and compression is good. So cylinders are safe! Took it to a shop finally. Had a bad MAF sensor and the person That did my header job put the O2 sensors back in wrong. Plus before I had any work done, when I bought my IS last year I had a bad downstream o2 sensor. Also patched a hole in the cool air intake where someone had left the nut n bolt off the bottom of where the filter mounds to a bracket so it was vibrating against something and made a hole on the intake, that’s patched now. You your right on most of what was wrong with it man, thank you!
 
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