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lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 9974
Experience:  Master Certified with lexus, 8 years experience with Lexus
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I have a 91 lexus ls 400. It has an intermittent problem.

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I have a 91 lexus ls 400. It has an intermittent problem. Sometimes when I give it gas it will not accelerate, then will accelerate abruptly. I ran a diagnosis on my check engine light and it said mass air flow sensor. I replaced that but the problem exists. Any advice as to were to start next? Thanks
Hello and thank you for using just answer. What code # XXXXX #'s are storing?
Customer: replied 9 years ago.
I don't really know. The people who read the code said it was a mass air flow meter or sensor. I changed that and it is still happeneing.
Thank you for your reply. There is no code that states "replace mass air flow meter". This may have been an unneeded expense. To avoid flying blind and replacing costly parts a little diagnostic work will be needed here. If you can get me the codes I can better assist you, it would not be fair for me to try to diagnose/or give advise on a condition that has a check engine light without the code #'s.
Customer: replied 9 years ago.
I will try and get the codes ran again and reply tomorrow. Thanks

There is a procedure you can do to get the codes your self if you feel capable and want to give it a shot, if not then reply back tomorrow and I will be glad to assist you. Thank you.

Customer: replied 9 years ago.
I would love to give it a shot. What do i do.

Ok, take a look at this:



Basically you will use a wire or a paper clip and cross 2 terminals in either the dlc connector under the hood OR under the driver dash and turn the key to "on" and cound the flashes.

Customer: replied 9 years ago.
I talked with the guy who checked the code. He said it was 21,22, or 24. Which ever says air flow meter. This was the only code it gave.
"21,22, or 24" ....OR...not sure perhaps??? These older LS' have very limited codes and unless the code #'s provided are 100% accurate I could majorly mislead you here. What I recommend is you look at the download I provided last night, remove the key, pull the EFI fuse for a couple minutes and then reinstall and drive the car until the light comes back on, then pull codes again and be sure. Sometimes certain codes will trigger other codes-this is why I want you to pull the fuse to reset the computer so we can get a fresh start on this and accurately trace it. Thank you.
Customer: replied 9 years ago.
I will do it this afternoon.
Thank you, XXXXX XXXXX your trouble but I want to be sure I ACCURATELY help you here. I look forward to your reply, have a great afternoon!!!
Customer: replied 9 years ago.
I pulled the efi fuse about three minutes. Started the car and the engine light came on immediately. Turned off car took paper clip to e1 and te1 as shown. It gave me a 2-5 code about 5 times in a row. Two blinks, a pause and then 5 blinks. Hope this helps.

Great Job and thank you! Code 25 is an air-fuel ratio lean malfunction. The ECM compensates and makes the car run rich when this happens. SEVERAL possibilities here. Take a look at this:



I would probably start by looking for obvious wire issues here. If the light comes on immediately after starting then you have a dead short or open here. Take a look at the oxygen sensors and see if you can tell if anything is obviously wrong. The diagnostic flow chart needs to be followed to trace this. The mechanic that just threw a part at the probelm (and a very expensive part!) was wrong for doing this. Air flow meter issues are not common on this setup, that's why they are so expensive.

Customer: replied 9 years ago.
Is this something I can do? Or do I need help? You have helped a lot so far.
Yes you can do alot of this with a simple digital volt ohm meter. Read the downloads I have posted, it has the check procedure in the last download I posted. Basically you need to check some voltages to see if the problem can be identified.
Customer: replied 9 years ago.
I received your message. I am definately going to pay you. I have been trying to do what the paper says this morning but am not sure if I am doing things right. When it says to connect te1 and e1 is that done under the hood or in the dashboard. If Icheck it under the hood my voltmeter doesen't fit to well. I am a little new at this voltmeter stuff. Any helpful suggestions?
THe connector under the dash AND under the hood are the same, I find it is easier to use the under hood connector.If you are jumping the terminals to read codes I usually jam a paper clip in the 2 terminals or have an assistant hold it in so I can read codes. Volt meter just make sure you have a god connection at the 2 connection points. I will be offline for a couple hours here so reply back with any findings/questions. Thanks
Customer: replied 9 years ago.
I am looking at page TR-63. Middle of page says *1 when diag.code 25 or 26 is displayed go to step 7. Then step 7 says to check each circuit. Then it shows me the page numbers to the left of the description. I don't have these. Where do i find these and which ones should I use. I am trying but not having much luck.

Sorry for the delay, code 25 and 26 are the only ones stored right?

Here are the first few to check as you requested:

Download1 IG-6

Download 2 Tr-121


EM-31 is too large to upload, it calls for checking the timing belt position but you should have a code 13 also if this was an issue.


Customer: replied 9 years ago.
I think I am going to have to take this to someone, unless you think I should change the oxygen sensor. Were is this located?
Threre are 4 o2 sensors on your car and quite pricey, there is one on each ehhaust manifold just before the connecting pipe and there is 2 sensors just after each catalytic converter, the wires for the rear ones come through the floor about where your feet rest in the front. I was hoping you could trace this down to avoid a diagnostic charge, an o2 sensor is a likely failure here but unlike your initial repair I don't want to advise you to replace any expensive parts until they are verified bad.
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