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1990 Ls400 At 45-50Mph


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Hi everyone,

my LS400 stutters when I try to hold 45-50mph. I just push the gas lightly to hold that speed and the car stutters. I guess this is the right term. I have no problem at higher or lower speeds, and it does not do when I floor it.

I have a small leak at the back of the left side valve cover, can it cause this?

Thanks

A

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Hi,

You don't state the year of your LS but even if there is no dash warning light for the engine management system I would read the fault codes to see if anything is coming up.

The vacuum pipe does need attention but is unlikely to be the cause of the problem.

The most probable cause is the TPS mounted on the throttle body,the electrical tracks in this do wear and the wear is normally at a constant cruising speed point.

Symptoms of a Defective Throttle Position Sensor

Following is a list of symptoms, either of or a combination of which, a car driver may experience because of a defective throttle position sensor:

Bucking and jerking of the car

Idle surging

Sudden stalling of the car engine

Hesitation while the driver of the car is trying to accelerate

Sudden surge in car's speed while driving on the highway

post-26370-127560002069_thumb.gif

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Hi everyone,

my LS400 stutters when I try to hold 45-50mph. I just push the gas lightly to hold that speed and the car stutters. I guess this is the right term. I have no problem at higher or lower speeds, and it does not do when I floor it.

I have a small leak at the back of the left side valve cover, can it cause this?

Thanks

A

A throttle valve cleaning might solve your problem. My vehicle had the same sounding issue that was corrected with a good cleaning of the throttle body.

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  • 1 month later...

Thanks for the replies. It turned out that the previous 'mechanic', who did the tune up didn't push the spark plug wires correctly, so they cracked, became wet, etc. so they needed a replacement, and also, he put cheap

spark plugs instead of the right ones.

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