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04 IS300 automatic
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Discussion Starter #1
Hi so this is my first time on any forum discussion so bare with me! I love my IS so much that I’ve spent 4K in the past 9 months(bought it from a friend last year) to maintain it. Currently my first gen has almost 260k mikes on it. The cats rattling was about to drive me insane, it was running sluggish and I didn’t really wanna spend 1,200 on a new manifold so I went with header. Well the gasket was a POS and fell out. The person that did it put my old gasket on.then I had to pay a muffler shop to put a bung and weld last o2 sensor on bc was too close to firewall. Ever since I had this done it seems to run super rich and I hate it now! Drives like the tranny is about to go out. Cruise control doesn’t work right and my trunk feels almost too hot to touch not to mention the smell coming through vents or with windows down give me a headache! I’m torn between getting rid of it or keeping it as a project car. Thing is it’s my daily driver rn and I’m done pouring money into this car especially if the end result is-runs and Sounds like POS. Someone please help me here!!
 

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If you removed all 3 cats, did you simulate the rear o2 sensors or do you have cel codes? If you have codes, what all codes are you having to start. Also watch your postings. You have asked about the gasket is two places and this is against the rules.
 

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2002 Lexus IS300
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solar is correct about using spacers to get rid of cat codes. As far as smells, just get a new exhaust manifold gasket. They are cheap. Unless you have an oil leak, that will smell too.
 

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04 IS300 automatic
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Discussion Starter #5
If you removed all 3 cats, did you simulate the rear o2 sensors or do you have cel codes? If you have codes, what all codes are you having to start. Also watch your postings. You have asked about the gasket is two places and this is against the rules.
 

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04 IS300 automatic
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Discussion Starter #6
Ok ty, didn’t realize there are rules...I live in Tn and there are no restrictions on emissions. Only removed 2 of 3 cats and I’m thinking O2 sensors were placed wrong. Thanks for the reply
 

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Ok ty, didn’t realize there are rules...I live in Tn and there are no restrictions on emissions. Only removed 2 of 3 cats and I’m thinking O2 sensors were placed wrong. Thanks for the reply
The two down stream O2 sensors you can space them out or get an electronic simulator. If you got rid of the manifold. Do not forget the down-pipe has one that can get clogged.
 

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solar is correct about using spacers to get rid of cat codes. As far as smells, just get a new exhaust manifold gasket. They are cheap. Unless you have an oil leak, that will smell too.
Make sure you get the factory MLS (multi-layer steel) ones, they're really good gaskets compared to the...other ones. I have no idea what they're made of, but they wont last
 

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04 IS300 automatic
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Discussion Starter #9
solar is correct about using spacers to get rid of cat codes. As far as smells, just get a new exhaust manifold gasket. They are cheap. Unless you have an oil leak, that will smell too.
Well I know the difference in smells of rich exhaust and burning oil. PO175 running too rich “Bank 2” is the OBD2 reading and beforehand it was misfiring on 4 repeatedly so had coils n plugs replaced. After I had all that done as soon as engine light came on again it started driving like a POS again. Bad O2 sensor???
 

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2002 Lexus IS300
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Well I know the difference in smells of rich exhaust and burning oil. PO175 running too rich “Bank 2” is the OBD2 reading and beforehand it was misfiring on 4 repeatedly so had coils n plugs replaced. After I had all that done as soon as engine light came on again it started driving like a POS again. Bad O2 sensor???
Oh sorry I misunderstood this. I didn’t think it was running so rich that raw fuel smell was the issue. If you have a scanner that can read live data, I would monitor the upstream o2 sensors on BOTH banks to see what they are doing. I would also monitor the MAF sensor and IAT and ECT sensors.

Does it run fine on a cold start up and then gets worse as it warms up?
 

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04 IS300 automatic
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Discussion Starter #11
Oh sorry I misunderstood this. I didn’t think it was running so rich that raw fuel smell was the issue. If you have a scanner that can read live data, I would monitor the upstream o2 sensors on BOTH banks to see what they are doing. I would also monitor the MAF sensor and IAT and ECT sensors.

Does it run fine on a cold start up and then gets worse as it warms up?
It’s hard to see a pattern, cold start or not doesn’t seem to matter much. it’s more like when I’m at a full stop and then need to pull out into traffic it barley sputters then all of the sudden bam! 5k rpm..had sensors and throttle body cleaned out which was filthy from running rich. Sensors on these cars are not cheap. Did the header as apposed to Manifold with cats replace to save some money and make car a little more zippy, that’s been a hard fail.
 

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2002 Lexus IS300
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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.
 

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04 IS300 automatic
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Discussion Starter #14 (Edited)
Do the live scan and make suure the primary O2 sensors are reading quickly and correct. If they are, it may be leaking injector.
It’s hard to see a pattern, cold start or not doesn’t seem to matter much. it’s more like when I’m at a full stop and then need to pull out into traffic it barley sputters then all of the sudden bam! 5k rpm..had sensors and throttle body cleaned out which was filthy from running rich. Sensors on these cars are not cheap. Did the header as apposed to Manifold with cats replace to save some money and make car a little more zippy, that’s been a hard fail.
yes you are correct about on a cold start it running well. Notice at night when it’s not as hot and I start it, response time is immediate. When it’s hot out it sputters until the pedal is to the floor then it takes off for sec and hesitates again.
 

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04 IS300 automatic
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Discussion Starter #15
The smell is because you removed the cats. The way to fix all of your problems is to replace all of the exhaust with new stock parts.
This isn’t a small smell, it’s running so rich n misfiring that it fucked my spark plugs. Think downstream o2 and MAF sensor need replacing and going to maybe put a simulator on downstream since cats are gone and it’s expecting a totally different gas/oxygen ratio.
 

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04 IS300 automatic
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Discussion Starter #16
This isn’t a small smell, it’s running so rich n misfiring that it fucked my spark plugs. Think downstream o2 and MAF sensor need replacing and going to maybe put a simulator on downstream since cats are gone and it’s expecting a totally different gas/oxygen ratio.
It’s also giving me a headache. It’s not normal what I’m smelling And definitely probably not going to spend thousands on factory parts that’s the entire reason I’m on here.
 

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Discussion Starter #18
This was ran after replacing all 3 coil packs and spark plugs were replaced
 

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04 IS300 automatic
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Discussion Starter #20
If you removed all 3 cats, did you simulate the rear o2 sensors or do you have cel codes? If you have codes, what all codes are you having to start. Also watch your postings. You have asked about the gasket is two places and this is against the rules.
Solar Yellow you have been really great, at least giving me the time of day that I haven’t been getting from the guy that put this header on. And I’m stuck now bc shops aren’t supposed to really mess with mods like that. Think downstream o2 and MAF sensor need replacing and going to maybe put a simulator on downstream since cats are gone and it’s expecting a totally different gas/oxygen ratio what do you think?
 
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