96 lexus ls400. Car idles high and runs rough until competely warmed up then seems to run normal. I'm worried this could be stressing the engine out ? Not sure what it could be, I thought when your idle control valve was bad your car would idle too low, could this be a sensor ?

I doubt it.
Probably a vac leak or problem with the throttle body.
The engine computer controls idle speed.

May be its low on coolant or radiator hoses clogged or its thermostat issue,its remaining closed or it can be issue with coolant leaking from somewhere.Or cooling fan not running when when engine gets warm.
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There are many other possibilities causing these issues.:----
To troubleshoot the issue yourself,i provide you few very helpful links with solutions:-----
Click the link below:----

Dodge Dakota stalls, stumbles at idle. Has low fuel flow and runs hot?

http://schematicsdiagram.blogspot.in/2012/03/dodge-dakota-stallsstumbles-at-idlehas.html

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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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1995 Lexus LS400: Running Hot?

http://whatisbyme.blogspot.in/2012/05/1995-lexus-ls400-running-hot.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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There are many possibilities for car overheating.

Faulty thermostat clogged radiator/plugged radiator, radiator hose worn out. Coolant running low. Low coolant pressure. Faulty temperate sensor.

I suggest you to go through the troubleshooting details mentioned in the link below:-----

All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html

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These will help.

Thanks.

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.

First. Storing anything that is Gasoline powered for a long time ( typically over 6 months) should have a full tank of fule with Stabil or simmilar product in the tank and fog the engine. ( inducing a engine fog according to product lable)
As for your car I show that the Lexus LS400 has no external fuel filter. ( Poor Choice by Toyota in my opinion) the only filter that AllData shows for your car is in the fuel tank. If you have not *** of yet. I would find a place that sell Castle FireBall. It is the best injector and fuel system cleaner I have found. Try that first. If no luck you may have to try a professional injection cleaning. That would be my first try, if you have ruled out vacuume leaks. Letting a car sit can also cause dry rot of vacuume lines. Look it over good. Spray carb cleaner while engine is running on vacuume lines and see if you hit a spot where engine smooths out. if so that is a sure sign of a vacuume leak in that area.

CHECK YOU'RE catilactic converter

The first thing I would do is remove the hose connected to the intake and see if there isa lot of blackish brown buildup on the plate, if there is you need to buy some top engine cleaner and with a tooth brush clean the throttle plate on the back side and also the pipe that it sits in. Over time Gum builds up from back fires that you can't feel and causes the plate to open up and gradually will cause this problem.
Check this first and if you find that it is dirty then let me know and I will tell you how to do a top engine clean to get it running better, I do this in a order that won't cost you as much. If there is build up in the engine it will also cause the engine not to get good fuel mileage. Check this first and let me know so I can help you save money, you can do the top engine clean yourself. As far as sensors go I do the simplest things first before moving on to the sensors.

check the coolant temp sensor very common problem on these cars

1993 Lexus LS400 wont idle but will run

seem like you got the same problem as my scion xa, check the fuel pressure regulater. bad regulater some time smell like leak gas. auto zone might cause you about $80.00.