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Discussion Starter · #1 ·
I recently bought a black 2001 is300 and have started to fix some of the issues that it has. This car has gone through a lot of peoples hands before me and definitely has its issues. The biggest one I'm currently facing is the car is running 38% lean on long FT bank 1 and 2 and they consistently stay between 3% of each other. I replaced the MAF with an OEM Toyota one that brought it down from 48% to 38% but still facing the issue. I believe it to be a wiring issue from the MAF to ECM or something correlated, I did a smoke test on my intake and there was no vacuum leaks. It starts completely fine when cold and once its running and idling for a couple minutes its typically fine. I find the most issues on warm or operating temp starts where it will cranks start and then have an extremely low idle and die out before the 02 sensor and ECU can start adding fuel to correct the lean where it then sits at about 34-39% lean. I'm a tech student and have facilities to run tests and diagnostics as well as pulling procedures and diagrams this issue has left me and my teacher stumped thus far. He believes it to be fuel system related but we don't know where to start because it seems there's no test port on the OEM fuel rail to test fuel pressure. Only codes that show are pending lean FT codes, if anyone has faced this trouble in the past any guidance would be greatly appreciated. Thanks.
 

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Discussion Starter · #2 ·
I recently bought a black 2001 is300 and have started to fix some of the issues that it has. This car has gone through a lot of peoples hands before me and definitely has its issues. The biggest one I'm currently facing is the car is running 38% lean on long FT bank 1 and 2 and they consistently stay between 3% of each other. I replaced the MAF with an OEM Toyota one that brought it down from 48% to 38% but still facing the issue. I believe it to be a wiring issue from the MAF to ECM or something correlated, I did a smoke test on my intake and there was no vacuum leaks. It starts completely fine when cold and once its running and idling for a couple minutes its typically fine. I find the most issues on warm or operating temp starts where it will cranks start and then have an extremely low idle and die out before the 02 sensor and ECU can start adding fuel to correct the lean where it then sits at about 34-39% lean. I'm a tech student and have facilities to run tests and diagnostics as well as pulling procedures and diagrams this issue has left me and my teacher stumped thus far. He believes it to be fuel system related but we don't know where to start because it seems there's no test port on the OEM fuel rail to test fuel pressure. Only codes that show are pending lean FT codes, if anyone has faced this trouble in the past any guidance would be greatly appreciated. Thanks.
^^^^^ I personally think its head soaked and chaffed wiring that shorts when it expands once its hot but I don't know where to look on the harness for it. If anyone has had experience with that let me know!
 

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2001 Lexus IS300
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I recently bought a black 2001 is300 and have started to fix some of the issues that it has. This car has gone through a lot of peoples hands before me and definitely has its issues. The biggest one I'm currently facing is the car is running 38% lean on long FT bank 1 and 2 and they consistently stay between 3% of each other. I replaced the MAF with an OEM Toyota one that brought it down from 48% to 38% but still facing the issue. I believe it to be a wiring issue from the MAF to ECM or something correlated, I did a smoke test on my intake and there was no vacuum leaks. It starts completely fine when cold and once its running and idling for a couple minutes its typically fine. I find the most issues on warm or operating temp starts where it will cranks start and then have an extremely low idle and die out before the 02 sensor and ECU can start adding fuel to correct the lean where it then sits at about 34-39% lean. I'm a tech student and have facilities to run tests and diagnostics as well as pulling procedures and diagrams this issue has left me and my teacher stumped thus far. He believes it to be fuel system related but we don't know where to start because it seems there's no test port on the OEM fuel rail to test fuel pressure. Only codes that show are pending lean FT codes, if anyone has faced this trouble in the past any guidance would be greatly appreciated. Thanks.
I also have a 2001 with a lot of wiring issues one including my MAF. My car was also running too lean for awhile and after replacing just the censor it fixed the lean issues. I would have your MAF rewired as well but I would pay for a dealership to do it because anything else (for me) has proven not to work. I also would check all your 02 censors, and to make sure your fuel pump isn't bad and is priming and working how it should be.
 
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