Lexus LS400 loss of power and excessive fuel consumption and rough or low idle speed. HELP!!

Check the level of coolant

OBD Tools 365 Days Shop
A rough engine idle can come from a variety of causes. During the winter months, cars may have a harder time starting and will shake when first turned on. This form of rough idle can easily be mistaken for other problems. Engine idle problems can also be attributed to malfunctioning components, such as spark plugs. Holes in the air intake valve can also cause a rough engine idle because of excessive amounts of air being drawn in.
The rough idle of an engine can signify a power loss in the car. This loss of power could lead to other problems, such as excessive gas consumption. This lack of power can also lead to additional wear on other parts of the car. Ignoring problems with the engine of can lead to a massive breakdown that will require you either to make costly repairs or replace the car entirely.

spark plugs injector cleaner have u been runing with low fuel pump may be on it way try fuel injector cleaner & fill tank 90 plus octane

Idles rough and quits when gas pedal is pressed less?
http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html
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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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Its a hot start issue.

Can be related to low fuel pressure or problem with crank sensor.

Also it can be weak battery or starter.

But possibilities are to be inspected to confirm what exactly it is.------

To troubleshoot and confirm the issue,i suggest you refer few solved help links with similar types of problem like yours:------

Click the link below:------

1991 Toyota Trecel: Engine Starts fine but dies when gets Warm?

http://whatisbyme.blogspot.in/2012/05/1991-toyota-trecel-engine-starts-fine.html

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1994 Toyota Pickup: Starts fine but dies in few seconds?

http://howtobyme.blogspot.in/2012/05/1994-toyota-pickup-starts-fine-but-dies.html

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1995 Lexus LS400: Running Hot?

http://whatisbyme.blogspot.in/2012/05/1995-lexus-ls400-running-hot.html

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2002 Toyota Camry: Puff of Blue or White Smoke while Starting?

http://whatisbyme.blogspot.in/2012/05/2002-toyota-camry-puff-of-blue-or-white.html

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Multiple problems on car: Car runs hot, A/C blows hot and car starts surging?

http://schematicsdiagram.blogspot.in/2012/04/multiple-problems-on-car-car-runs-hotac.html

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Delay starting on Toyota Prius?

http://schematicsdiagram.blogspot.in/2012/02/delay-starting-on-toyota-prius.html

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Honda car will not start intermittently?

http://technoanswers.blogspot.in/2012/02/honda-car-will-not-start-intermittently.html

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Vehicle Starts, Runs and Loses Power

http://whoisbyme.blogspot.in/2012/07/vehicle-startsruns-and-loses-power.html

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Intermittent starting issues on Volvo 760?

http://schematicsdiagram.blogspot.in/2012/02/intermittent-starting-issues-on-volvo.html

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Car starts and cuts off immediately?

http://repairhelpcenter.blogspot.com/2012/01/car-starts-and-cuts-off-immediately.html

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Car won't start when cold?

http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-when-cold.html

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These details will help.

Thanks.

It can be issue with low fuel pressure,the fuel pump is getting old both needs to be checked.Also get the IAC valve checked.
Go through the related help links with similar problem,it may help:---
Click the links below:---
Engine Idles Rough and Dies? http://whatisbyme.blogspot.in/2012/05/1994-lexus-es300-engine-idles-rough-and.html

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van idles rough? http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html

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runs lean and idles rough? http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html

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Car still runs Rough after tune up?

http://howtobyme.blogspot.com/2011/12/car-still-runs-rough-after-tune-up.html

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2006 kia rio runs rough http://technoanswers.blogspot.com/2012/10/2006-kia-rio-runs-rough.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed? http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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Rough idle, staling and Erratic shifting? http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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These details will help.
Thanks.

these vehicles are known for ignition coil failure. typical symptoms include: Misfire, power loss, vibrating engine, poor fuel consumption. If the vehicle's engine vibrates, it be misfiring. Is your chk engine light on???

It could be a idle air valve, a loose, unplugged or missing vacuum hose or a throttle position sensor.

check the coolant temp sensor very common problem on these cars

It sounds like a fuel delivery issue so it could be many things such as low fuel pressure from the pump,clogged or partially pluged fuel filter, a malfunctioning throttle posisitioning sensor (if you have a check engine light on) or if its turbo it could be turbo lag etc.

You just go to the link I attached I'm sure you will get the solution of your problem 1991 LS400