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Discussion Starter · #1 ·
So I’ve been dealing with misfire issues for a while and I’ve replaced many things, eventually I found my compression too be low due too stuck piston rings but I managed too get them free with marvel mystery oil and now my engine has good compression again. But I still have random misfires and my idle is high until the engine warms up too operating temperature. when I was looking at the live data on my obd I noticed both bank 1 and 2 secondary o2 sensor voltages we’re fluctuating very low, generally staying below 0.1volts and I also noticed short term fuel trims in the 90% range for b1s2 and b2s2. Aside from this my other short term fuel trims were negative but less concerning sitting around -10%. I’m just wondering if this low o2 sensor voltage could be causing the issue with fuel trim and possibly the misfires or if it’s more likely a issue with my fuel injectors or MAF. Any suggestions help thanks!
 

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Discussion Starter · #3 ·
Ya the entire engine is stock other than a high flow air filter. I also checked for totally clogged fuel Injectors but when I listened too the noise each made individually they all sounded like they were firing at the proper rate so what could be causing this crazy fuel trim? Could it be caused by the misfire?
 

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Is it just a different filter or is it the whole filter box and pipe? I know some have fuel/air issues when they replace the whole pipe and box as the air doesnt flow over the MAF the same way as it is supposed to.
 

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2002 Lexus IS300
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Ok, forgive me but I actually just took the time to read your entire post and noticed you said it idles high until it reaches operating temp.

What are your upstream O2 sensors doing when cold, warmer ~100 degree ECT and fully warm?

you could have a pretty serious air leak somewhere that is actually sealing itself up as the motor warms up and the metal expands. This is extremely common on the Gen. 3 LS engines with intake manifold gaskets and P0300 codes.
 

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Discussion Starter · #11 ·
I don’t smell gas and the gasket between the manifold and the intake air connector (y pipe for the intake) is new, I put it in with the beveled lip facing the throttle body as I thought this was the correct orientation. The oxygen sensor readings (only b1 s1 and b2s1) seemed to get slightly better but not by anything extremely noticeable it just seemed to refresh below 0.1 v less, also noticed they would hangout below 0.1v for 2 or 3 refreshes when it was cold aswell (this would rarely happen when it was hot) but I’m not sure if this is a issue with the sensor or if this is just because of the misfiring/air leaks. My fuel trims seemed noticeably better when hot though, when I ran the engine from cold my b2 fuel trim sat around -17% and b1 around -6% but when I reset the ecu well the engine was hot and tried running it again both seemed to stay around -6% give or take after a bit of idling. This seemed odd too me though because wouldn’t the fuel trim be positive if unmetered air was entering the intake?
 
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