Thread #16705

LS400 running like crap-please help

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RunninWildMarch 26, 2009

LS400 running like crap-please help

I'm still in 101 so I have to post this here.

I was travelling along in my Lexus LS400 with it running nice and smooth and came to a stop at a light. I proceeded to accelerate but my tach dropped to 0 rpms with the engine still revving out. The tach started to come up after I lifted off the gas and got back on it but once it hit 1,200 to 1,500 rpms it dropped to 0 again but the engine kept revving agian.

The car has a slightly rough idle now and shutters when I first get on the gas from a stop. It has no power at all and no matter how much throttle I give it it feels like I am giving it 1/4 throttle. It will rev out to high rpms in first gear and shift hard no matter how much throttle I give it either. It has plenty of trans fluid in it. Just sitting at idle the cats become red after it has been idling for a couple of minutes. Oh and when I rev it up doing a dry rev it wraps up waaaay slower than before.

Also, it has not thrown any CEL's.

If anyone has any idea on what might be wrong your input will be greatly appreciated=)

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I'm still in 101 so I have to post this here.
 
 
 
I was travelling along in my Lexus LS400 with it running nice and smooth and came to a stop at a light. I proceeded to accelerate but my tach dropped to 0 rpms with the engine still revving out. The tach started to come up after I lifted off the gas and got back on it but once it hit 1,200 to 1,500 rpms it dropped to 0 again but the engine kept revving agian.

The car has a slightly rough idle now and shutters when I first get on the gas from a stop. It has no power at all and no matter how much throttle I give it it feels like I am giving it 1/4 throttle. It will rev out to high rpms in first gear and shift hard no matter how much throttle I give it either. It has plenty of trans fluid in it. Just sitting at idle the cats become red after it has been idling for a couple of minutes. Oh and when I rev it up doing a dry rev it wraps up waaaay slower than before. 

Also, it has not thrown any CEL's.

If anyone has any idea on what might be wrong your input will be greatly appreciated=)

drftsubMarch 28, 2009

#238657

well, it seems as if it has lost something that would trigger RPM signal, which could do all of those things, but it would also seem that if it were something like a crank/cam sensor TOTALLY out it would throw a code. There is a possiblilty that its simply a short in the wire that feeds RPM , some run through the cluster then down to the ecm/tcm ( engine control and trans control ) which may do it as well. You may have an intermittent fault ( which are always the largest PITA to diagnose ) but I would check the signal wire then those two sensors, problem is you really need a scope to do it. If you have access to one back probe the signal wires to see if there is a consistent signal, I don't know if that car has a hall effect or magnetic style sensor on it so I couldn't tell you the specific waveform you are looking for but if you can find a PDF of the factory manual it should tell you. Thats about as much I can suggest as a starting point without having the car in front of me.

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well, it seems as if it has lost something that would trigger RPM signal, which could do all of those things, but it would also seem that if it were something like a crank/cam sensor TOTALLY out it would throw a code. There is a possiblilty that its simply a short in the wire that feeds RPM , some run through the cluster then down to the ecm/tcm ( engine control and trans control ) which may do it as well.  You may have an intermittent fault  ( which are always the largest PITA to diagnose ) but I would check the signal wire then those two sensors, problem is you really need a scope to do it. If you have access to one back probe the signal wires to see if there is a consistent signal, I don't know if that car has a hall effect or magnetic style sensor on it so I couldn't tell you the specific waveform you are looking for but if you can find a PDF of the factory manual it should tell you. Thats about as much I can suggest as a starting point without having the car in front of me.