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Boxer54, ASE Certified Technician
Category: Lexus
Satisfied Customers: 1755
Experience:  Over 15 years experience in automotive field - ASE master technician and L1 advanced certification
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91 Lexus LS400: a diagnostic..running rough..low idle..air flow meter

Resolved Question:

I have a 91 Lexus LS400. Recently I had a mechanic run a diagnostic on it because it was running rough, low idle, no power and I couldn't get it up to speed. He said it indicated it needed a new air flow meter. I put another one on it and it ran great. Then just recently it started running in a similar manner. It ran perfect to my work, but when I started it up to go home in the evening: Low idle, no power, smoking out the exhaust. It was the same as before except it is not running rough. Smooth but now zip when you give it the gas and smokes like very rich air fuel mixture. I changed the air flow meter again and it still runs the same. It feels and seems like air fuel mix as before. Not sure where to go next?
Submitted: 5 years ago.
Category: Lexus
Expert:  Boxer54 replied 5 years ago.
Thank you for trusting Just Answer with your Lexus question. Do you have a check engine light on?
Customer: replied 5 years ago.
No check engine light on. It starts but when running you have to feather the accelerator to keep it going and it won't idle without stalling out. It will raise in rpm gradually, slowly. Doesn't miss fire.
Customer: replied 5 years ago.
did you get my reply?
Expert:  Boxer54 replied 5 years ago.
Sorry, I was offline yesterday. This sounds most like a fuel pressure issue. You need to have the fuel pressure checked to make sure, but moat likely a fuel pump.
Customer: replied 5 years ago.
Would this show up in a OBD1 test?
Expert:  Boxer54 replied 5 years ago.
Probably not. 1st generation OBD is not near as sensitive as OBDII. If you could watch the oxygen sensor voltage it may give you some clue to a lean condition, but that still doesn't condemn the pump. An actual fuel pressure test is needed here.
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