1993 LS400 Problems. Please HELP! - ClubLexus - Lexus Forum Discussion


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1993 LS400 Problems. Please HELP!

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Old 12-17-13, 04:23 PM   #1
tps3443
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Default 1993 LS400 Problems. Please HELP!

Ok, I have a 1993 LS400, I bought the car 2 weeks ago. It drove AMAZING the first 2 days. Then it would stumble on about 20% throttle and buck under acceleration. It has a rough idle, and it will not warm up much it all. It had a lot of white smoke, and it did not have a CEL light on.

The PS pump was new, and not leaking so, I elimated that as a problem for the white smoke. Because I read they do leak into the intake and burn the PS fluid. Mine, is not leaking.. So I changed the ECU to a good working used one from a 1994 LS400. And, no more white smoke. Now the CEL light is on for the Mass Air Flow sensor.

I replaced the MAF sensor, and the car runs the same, it bucks under acceleration. It will idle, and almost die under any kind of acceleration at all. It is running really rough. It has new plugs, wires, fuel filter, air filter, etc etc.

I really love this car, but.. I do not know what to do? I get about 5-7 MPG. And it runs like a 1950's dump truck with about 750,000 miles on it, that was started after sitting for 10 years.

Although, it is a Lexus with 243k miles that is really clean inside and out.


I have read so many similar issues like mine. But they are all so different as well.

My car idles at about 500 rpm, it is drinking gas really bad. I get about 5-10 mpg. When you press the gas to go, it wants to almost die out. And it will slowly accelerate and buck and stumble up to speed. My 0-60 is about 18-25 seconds

It will start everytime, but it idles rough, and it only throws a code for bad MAF sensor. it does not leak oil, or knock, or run hot, it actually will not get warm enough because it seems as if it runs to rich.

I just really want to fix this car.

When I pulled the old ECU out to change it. It has these same symtoms written on the ECU it self. And a name and a number. I called the number and the guy said he owned this car 5 years ago. and I am the 4th person to call with these same problems over the years. And that this lexus can never be fixed it is doomed for ever. And people keep selling it off and lying to the buyer.

I am frustrated, and it has just been sitting around. And I have been driving one of the dealers cars I work at.
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Old 12-17-13, 04:27 PM   #2
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The only thing I can think of is, fuel pressure? bad coils? The MAF is new. And it still throws a code for the MAF, I have reset the ECU, and tried driving the car for about 50 miles. Still no change. Plugs are new, and wires are new as well. I have cleaned the intake really well, I seafoamed the engine, and gas tank, and I used fuel system cleaner. I have tried all kinds of stuff. Still no luck.

I have tried adjusting the TPS sensor to help with the idle. And it did not help me much.
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Old 12-17-13, 06:03 PM   #3
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oh we can definitely get your LS straightened out, Club Lexus hasn't been stumped yet!

but you will need to run a few tests for us!

the fact that you changed ECU's and the symptoms changed somewhat, shows that the ECU is at least part of the problem, the ECU issue and how to fix it is discussed here. 93 LS400 is famous for these failing ECU capacitors! (all 90-97 are affected in epidemic proportions, especially here in the South)

you can also run Yamae's ECU ripple test and verify that both ECU's have issues

you can check the coils and igniters and associated wiring in a 1 minute test shown




make sure you are downloading and clearing the diagnostic codes in the proper way as shown here

you can buy a low cost but high quality fuel pressure tester with the correct Toyota banjo fittings and verify the fuel pressure

those steps should likely pinpoint the issue

Last edited by LScowboyLS; 12-17-13 at 06:08 PM.
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Old 12-17-13, 08:40 PM   #4
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sounds like an ignition issue, check all the plugs, wires, rotors, caps, and both ignitiors.
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Old 12-18-13, 12:21 AM   #5
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My 1991 LS had a similar problem stalling and rpm's running at 200-300 rpm I replaced both coils . and the problem disappeared. I had 298,000 at the time now over 300,000 no more problems. I also replaced the map sensor system from Lexus and it was expensive $920.00 I tried a junk yard unit it lasted 3 months so I bought new. Good luck with yours.

Last edited by Bill Dowd; 12-18-13 at 12:26 AM.
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