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  #1  
Unread 03-10-2009, 10:16 PM
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Default LS400 and SC400 Sputtering At Cruising Speed

THIS IS THE MOST ANNOYING THING EVER. I have looked ALL over for answers and there are a few people on the LExtreme.com type forums all looking for a definite answer to this problem. The problem? Yeah there are lots of instances of this model of car stuttering at cruising speed. They accelerate just fine when you punch it but if you just give it half throttle or less the car will act like it's misfiring.

Here is a post that I posted a couple of weeks ago:
I was invited to help a local mechanic shop troubleshoot an LS400 today and I worked on it for about 2.5 hours swapping out more parts and checking things over. Still the same symptoms as you have described. Very annoying and checking the mechanics database there are A LOT of other mechanics that have had the same problems!

It must be a wiring fault but I'll also be checking on that TPS the next time I give it another session. There is a LOT of heat in those stock LS400 engine compartments and it must just wreck the wiring. I know that almost any clip you decide to remove must be done with extreme care since all of the plastic breaks when you apply force to disassemble things.

Not fun but I'm pretty determined to help the poor soul that owns the car. Or maybe I should tell him it's a lost cause and offer him 500 bucks...
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Unread 03-10-2009, 10:21 PM
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I changed out so many parts on this customers car including the main computer . It simply can't be a module or component that has failed. I'm convinced that one of the wires has been toasted by high heat. I think the heat just degrades the wires over time and thus the wire then has more resistance than is acceptable. You might ask, "well then how come there are other people with the same problem?". I just can only say that those other cars have the same wiring in the same wiring harness position around the engine. I'm not a big fan of Lexus routing some of the wires for the ignitors so damn close to the water bridge on the front of the engine. Then look at the cam sensor wires as well. Those wires and others are just being cooked underneath all those covers around the engine.

That's why I'll be very cautious when I route all my wires in looms around my engine in my Tacoma. I'll probably run shielding around them all while I'm at it!
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Unread 01-10-2010, 10:08 AM
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Another problem area that causes the sputtering and surging at certain RPMs on the LExus SC and LS400 is the crank angle sensor. I've recently read of a guy who found his crank angle sensor wires to be in very poor condition. It's also funny that they are so small and weak yet they are in a fairly exposed position and are in a very harsh environment down there at the bottom of the engine.

So my advice is to rewire the crank angle sensor with some stronger wires and maybe sheeth them to give some added protection. I know mine is in great shape but if I had it off the engine again I would probably rewire it to make it stronger.
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