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Ok I have an 02 is300. Recently my cats were super clogged…

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Ok I have an 02...
Ok I have an 02 is300. Recently my cats were super clogged so I put some long tubes on. And drove for a day. While driving it felt the car turned into limp mode. Misfiring really bad loss of power until I passe 3k rpm then it feels like turbo or vtec. Typically if the car sits for awhile and gets super cold it tun for about 10min with no problems. Then it starts to bog/misfire. Code I’m getting is p0300 and random cylinder misfire codes. My other codes are for my post cat o2’s which is irrelevant atm. Bottom is the list of things I’ve replaced and still having the same issue. Now when I unplug my battery to reset the ecu it’ll run good for 5 min then goes straight back to misfiring and flooding the cylinders with fuel. Bank 1 short term fuel is reading lean and bank 2 short term fuel is reading rich. The exact opposite numbers. While all the long term fuel is all correct
Things changed.
Spark plugs
Injectors
Ocv
Maf
Coil packs
Wires
Tps
TPS motor
O2’s
Throttle body
Accelerator pedal sensor that is attached to the throttle cable
I’ve now came down to the only 2 things either ECU or engine coolant temperature sensor
Submitted: 4 months ago.Category: Lexus
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Answered in 6 minutes by:
12/13/2017
Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago
Robert R
Robert R, ASE Certified Technician
Category: Lexus
Satisfied Customers: 4,708
Experience: ASE Certifications in Engine Repair, Manual Drivetrain and Axles, Suspension and Steering, and Heating and A/C.
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Hello, welcome and thanks for asking your question. My name is*****'m a Certified Auto Technician with 30+ years experience. I will do my best to assist you. please keep in mind that I may need to ask questions of you before I can answer. When you reply please feel free to add as much detailed information as possible pertaining to your concern.

Coolant Temperature sensor sounds like it may be out of range. I would replace the coolant temperature sensor next BEFORE biting the bullet and getting the ECU...

Keep me posted and let me know if you have any additional questions...

Thank you,

Robert

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Customer reply replied 4 months ago
Gotcha I just think it’s so far fetched that the ect would be the issue just because when it’s in learning mode the car drives perfectly fine. After that it misfires and shakes the car really bad. A good friend of mine is also a tech and he looked in all data and all that and mentioned the diag procedures and mentioned only 2 I didn’t touch were the ect and ecu. But I’ll definitely get back to you. Correct me if I’m wrong there’s 2 sensors one that goes on the radiator hose and one on the block which is the one that reads for the computer. I also have screen shots and videos of the live data and of the car driving.
Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

Hello, sorry for the delayed response.

Actually, it makes even more sense that the ECT can be the cause because when the engine is in open loop "Learning Mode", the engine runs on a "preset" fuel map and doesn't necessarily use the data from all sensors until it goes into closed loop operation. In closed loop, the PCM uses data from several sensors in the fuel ratio calculation. If the coolant temp sensor is for instance sending a value of 50 degrees farenheit and the engine temp is actually 190 the pcm will see this 50 degrees and start richening the fuel mix (Engines need a richer mixture to run when cold than when hot). This excessive richening of the fuel mix can cause the misfires. This can happen both ways with the ect either causing too rich or too lean mixture...

There is only one ect that is tied to the fuel system, the other one is for the HVAC. The location of the correct sensor is near the power steering reservoir, see the following doc for location... --->> Click Here to view <<---

Keep me posted and let me know if you have any additional questions...

Thank you,

Robert

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Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

The fuel trim is controlled by the ECM using data from the upstream O2 sensors. The issue with yours being negative on one bank and positive on the other bank may mean that something is connected incorrectly or crossed. Is it possible that either O2 sensors or injector connectors may be crossed? If something is crossed, the PCM may be seeing this and making the fuel corrections to the "wrong side" causing the strange readings you are getting for the fuel trim..

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Customer reply replied 4 months ago
I’ll double check the o2’s, but I highly doubt it. If they are connected correctly what would you suggest next? I’m going to get the ect after work and replace that I’ll check the o2’s Since I’ll already be under the hood.
Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

Check for vacuum leaks, a vacum leak on one side can cause that bank to go lean and cause fuel trim to start adding fuel on that side..

Some O2 sensor brands can be inferior, what is the brand of the O2 sensors that you installed?

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Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

Can your scan tool monitor the coolant temp sensor value?

If so, I recommend to leave vehicle sit overnight. Then without starting engine monitor coolant temp with the scan tool and compare it to actual ambient temperature. If coolant temp value is greater than 10 degrees from ambient temperature then replacing the ECT should definitely help..

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Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

Anything less than 10 degrees probably wouldn't affect it much but any more than that will DEFINITELY make a difference. If the sensor is reading a negative temperature reading less than zero and the engine is at operating temp the engine would DEFINITELY run bad and likely be hard to start.

Your temperature at 91c is normal engine operating temperature (195f). To test the ect, let vehicle sit overnight and read the coolant temperature when engine is COLD and compare it to the outside temperature. This is the best way to test for proper ect operation.

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Customer reply replied 4 months ago
Gotcha I’ll let you know an update later.
Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

Thanks..

______________________________________

If you need additional information, don't hesitate to ask, I am happy to help as long as necessary to help solve your concern. Remember, a "Positive" Rating will not close this question, You can post a reply here whenever you want, even after rating my answer! .

Thank you!

Robert

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Customer reply replied 4 months ago
The ect works it was 37 degrees on the scanner this morning. I did not get a chance to check the o2’s Last night I should have time tonight.
Lexus Mechanic: Robert R, ASE Certified Technician replied 4 months ago

sounds good...

Keep me posted...

Thank you,

Robert

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