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P0171 & P0174 - poor mpg - stuttering

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Old 07-31-14, 01:22 PM   #1
mitchelltj
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Exclamation P0171 & P0174 - poor mpg - stuttering

Hey guys, I could really use your help. I'll try to make this as short as possible.

Had my transmission replaced with a used one from a Jap car. Although it shifts fine, within a few days got P0171/P0174 codes (fuel system too lean banks 1 and 2) and also an error for VSC that seems related to a front right speed sensor. Anyhow, I tried replacing the MAF (with a cheap ebay one) and fixing some exhaust leaks. Nothing helped. Then the car wouldn't start one day and sat for 6 months.

I had a mechanic get it running and he said it was just flooded and bellowed tons of smoke. He also checked for vac leaks and said he couldn't do anything more. The car drives weak for sure and sometimes sputs out visible exhaust when you step on the gas. Also has horrible mpg, stinks, and is slightly shaky especially at a light throttle. I'm at a loss but don't want to keep paying mechanics for things that aren't fixing it.

Any ideas? Fuel pump? Mystery vac leak? Something knocked loose from transmission install? Do I need a ECU or PCM update after the trans install? BTW there is still a small exhaust leak in front of the o2 sensor.

Thank you so much!
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Old 07-31-14, 02:43 PM   #2
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Hello welcome to clublexus! Anyways the first problem I spotted is that you installed a cheap ebay MAF air/fuel sensor (Big No No) any lexus models and many different makes usually tend to dislike the cheap Chinese trash I would suggest you go online and buy oem denso part (you should only use oem) also have your mechanic check your o2 sensors and make sure they are oem denso cause generic sensors will also cause a too lean problem good look!
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Old 07-31-14, 02:47 PM   #3
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Also I'm not sure if the Japanese transmission has different shift l
Points or ratio With gearing also if it's a awd in a fwd or vice versa maby a sensor left out or like you said it may need to be reprogramed to the ECU
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Old 07-31-14, 02:55 PM   #4
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Quote:
Originally Posted by mitchelltj View Post
Hey guys, I could really use your help. I'll try to make this as short as possible.

Had my transmission replaced with a used one from a Jap car. Although it shifts fine, within a few days got P0171/P0174 codes (fuel system too lean banks 1 and 2) and also an error for VSC that seems related to a front right speed sensor. Anyhow, I tried replacing the MAF (with a cheap ebay one) and fixing some exhaust leaks. Nothing helped. Then the car wouldn't start one day and sat for 6 months.

I had a mechanic get it running and he said it was just flooded and bellowed tons of smoke. He also checked for vac leaks and said he couldn't do anything more. The car drives weak for sure and sometimes sputs out visible exhaust when you step on the gas. Also has horrible mpg, stinks, and is slightly shaky especially at a light throttle. I'm at a loss but don't want to keep paying mechanics for things that aren't fixing it.

Any ideas? Fuel pump? Mystery vac leak? Something knocked loose from transmission install? Do I need a ECU or PCM update after the trans install? BTW there is still a small exhaust leak in front of the o2 sensor.

Thank you so much!
Sorry but dose the car shift into 4th gear or dose it revv at around 50 and dosnt shift also get carb cleaner and spray around vacuum hoses and air box and see if you get a change in idle
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Old 07-31-14, 03:03 PM   #5
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You need to fix your exhaust leak ahead of the O2 sensor. This leak can allow the sensor to see too much oxygen and it will interpret this as the vehicle running too lean (as your P0171,0174 trouble codes confirm). It will then try to richen up the mixture which the engine doesn't need, thus your bad smell and flooding problem.

x2 on the MAF sensor. Always use OEM sensors. No need to pay Lexus prices, they are available on Amazon.
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Old 08-01-14, 06:35 AM   #6
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Thanks for the thoughtful responses.

The cheap MAF I took out and put the original back in after resetting and finding that it didn't help at all. Should I still get a replacement?

O2 sensors are probably OEM. I put 30-40k miles on before I had problems.

The transmission is/was AWD and the car does shift into 4th, I think with no problem.

I'll check the vac lines with carb cleaner, good idea!

I guess next step is getting the exhaust hole fixed... I just don't want to go to Lexus or a foreign car expert and get taken. Prior to the transmission replacement, my rear exhaust was hanging off and I had no problems like this. Afterwards, I had it fixed, but it didn't change anything. Still, perhaps the hole near the front was created while pulling out the transmission and is giving me problems.
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Old 08-01-14, 09:01 AM   #7
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Okay great! Make sure the sensors are oem also the maf could be at fault, test the car this way to see if the maf is at fault, while the engine is running unplug the maf (try both original one and generic one) and if the engine respond and start running like crap the oem sensor is good, but if you unplug it and the engine doesn't do anything or respond the sensor is dead. Best of luck to you , and good luck!
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Old 08-01-14, 09:01 AM
 
 
 
 
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