The weather here in Indiana recently has droped (12 BELOW WITH WIND CHILL) since this has happened my LS400 now stays on high idle even after warm up is complete, I thought the throttle body may be gummed up so I went ahead and cleaned it thoroughly with no results ,can anybody help with this problem?

 

There are many factors that control the idle speed. I'd check that the ECU is getting the proper signals from sensors. The important first step is to check the voltage of the water temperature sensor. If it's higher than 2V after engine is warmed up, the problem may be caused by the sensor itself or the thermostat.

 

Yamae is right, as usual. The instrument cluster uses a different temp sensor than what the ECM uses. Check the voltage as Yamae described or hook up a tool capable of reading PID’s like a scangauge 2 and monitor the ECT.

 

Thanks guys for the info,as soon as the weather permits I will check the voltage at the sensor @ if correct I will change sensor.
I will also check out the thermostate while I'm there.

 

YAMAE first off THANK YOU for your suggestion that I replace engine coolant temp sensor , I also replaced my thermostate while I was there,
after doing so my HIGH IDLE problem is gone!
But . HA! after all this my Idle now is to Low in DRIVE POSITION ( I ADJUSTED THROTTLE CABLE AS THERE WAS SOME SLACK IN IT) also adjusted idle adjust screw ,this helped with idle in parked position (idle in park at about 7-800).
so how do I adjust the idle in Drive Position(right now it is at about 400-450) in drive.

 

The idle speed is controlled by the ECU. Of course other mechanical fundamental settings have to be done properly. I worry that you made those wrong.
Have you cleaned the IACV and the throttle body thoroughly?

One more item I need to confirm is that the ECU is OK. OK here means that the firmware is updated in accordance with the TIB and the ripple level is low enough. If not updated, it's too late to be done by the dealer for free.