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Starts fine and idles fine. revs normal in park. drives well…

Customer Question
Starts fine and idles...

Starts fine and idles fine. revs normal in park. drives well until gas pedal is pressed about 1/4 of the way down then it hesitates and jerks

Mechanic's Assistant: Has the vehicle turned into a gas hog? And how does it start -- same as usual?

Starts perfect. haven't noticed a huge change in gas mileage

Mechanic's Assistant: What is the model/year of your Lexus?

93 ls400

Mechanic's Assistant: Are you fixing your 9-3 yourself? What have you tried so far?

I have changed plugs and wires.... no difference

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Just that it runs great up to 2000 rpm in gear then engine just cuts out

Submitted: 27 days ago.Category: Lexus
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Answered in 17 minutes by:
3/30/2018
Lexus Mechanic: Matt, Engineer replied 27 days ago
Matt
Matt, Engineer
Category: Lexus
Satisfied Customers: 22,933
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
Verified

Hello and welcome to Just Answer

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

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Lexus Mechanic: Matt, Engineer replied 27 days ago

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 27 days ago
car runs great until gas pedal is pressed a bit more then it hesitates and will not go above 2000 rpm. car never dies and revs fine in park. it is not a fuel pump problem
Customer reply replied 27 days ago
it runs great when babying the gas pedal. but cuts out and causes car to jerk when pressing the gas a bit
Customer reply replied 27 days ago
In park there is no hesitation at all
Lexus Mechanic: Matt, Engineer replied 27 days ago

Hello

Ok this does all sound like a lack of fuel

please run through what I've described and let me know what you find

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Customer reply replied 27 days ago
If it was a fuel problem wouldnt it do it in park also?
Customer reply replied 27 days ago
When it cuts out it feels almost identical to the way electronic traction control cuts power from the engine to keep tires from spinning on my mustang
Customer reply replied 27 days ago
the traction control light is on.... is it possible it has something to do with the traction control?
Customer reply replied 27 days ago
I tried turning it off and it makes no difference. But could it be malfunctioning somehow causing it to activate?
Customer reply replied 27 days ago
The reason i dont think its a fuel problem is... the car will accelerate as long as the pedal isnt pressed hard. It will even go over 2000 rpm. But if you press gas pedal a hair further it cuts the engine and wont go above 2000 rpm exactly
Customer reply replied 27 days ago
The car has been to 2 different shops. First shop thought it was tps. It even seemed to solve the problem for aboutv10 minutes. Then same thing. Second shop checked fuel pressure checked lots of different things before giving up
Customer reply replied 27 days ago
I dont remember everything the 2nd shop checked. I will call him now so i can give you as much info as possible
Lexus Mechanic: Matt, Engineer replied 27 days ago

OK, assuming the fuel pressure is fine then it is possible its something to do with the traction control

as I've known a faulty wheel speed sensor to keep the system thinking a wheel is spinning when its not

ideally you would plug the car into a dealer level diagnostic device that can read the ABS and body control faults , as most generic scan tools won't do anything unless its an engine related code

you could also try pulling the ABS / DSC fuse to see if this helps

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Lexus Mechanic: Matt, Engineer replied 20 days ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Matt
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Category: Lexus
Satisfied Customers: 22,933
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Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.

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