help please, is there any way I can change the high idle I have on start up-1900 rpm. have replaced the temp sensor but that may a difference at 1st but i'm back to square one

 

You need to provide as much info as you can bro... For all we know you're talking about your weed wacker...

Year? Which temp sensor? What brand sensor? Any codes? Yada yada yada

 

Car is a 94 ls400 and the temp sensor from toyota has green plastic surround

 

Okay high idle at start up. So then what? Since we are not standing next to or sitting in the car all we can go on is what you tell us.
If it did funny things after a 10 minute warm up then I'd suspect things like that temp sensor, but since its doing high idle at start up the cold starting all seems to be fine to an extent. So the temp sensor is not even in the equation. I would suspect the idle air control but if it runs nice after warm up then that is probably not the problem.
As a guess one thing that does affect the before closed loop stuff is the basic program in the ecu, and that means a possible ecu problem, maybe the bad capacitors.
And are we sure the tachometer is reading the accurately?
And like Banshee says check the codes, you don't need a code reader to do it.

And just use a paper clip not a big wire like in the photo.
http://www.lexls.com/tutorials/intro/codereading.html

 

ok,the car starts up at 1900 rpm and warms down after 10mins or so.when I 1st changed the temp sensor, undid the battery and pulled the ecu fuse then the car would start at 1100 rpm. got up the next day and it had gone back to 1900 rpm on start up. once the car is warm it idles around the 600 rpm mark and there is no probs with driving.where is the ecu panel and bad capacitors hide?

 

https://www.clublexus.com/forums/ls-...capacitor.html

This tells it all.

 

I agree, ECM.

How does it rev when it's idling high like that? Does it seem to restrict itself in RPM's? Pull your ECM out and CAREFULLY disassemble it. Check the bottom of all of the capacitors for leakage of some gooey stuff. But keep in mind that not all bad capacitors leak. They can be sealed and still bad.

Your engine coolant temperature sensor is what's known as a negative temperature coefficient sensor. It's pretty much a thermistor. Your ECM sends the sensor a reference voltage of 5V. The computer then looks at how much voltage was lost after passing through the thermistor. It knows based on the voltage after the sensor what the temperature of the coolant is. It's pretty darn accurate too. The engine coolant temperature circuit can be GREATLY affected by bad capacitors as the ECM will then send out a reference voltage other than 5V. It will send out, say, 8V instead. You can obviously see how this would skew everything having to do with that circuit.

But, even worse, the bad capacitors in the ECM affect many many circuits, not just the ECT circuit. It will cause all sorts of wacky behavior. The last action in most of the engine DTC flow charts, after different tests and such, simply say's "Replace ECM." Luckily they are rebuildable at a pretty affordable cost.

 

Make sure to double check your intake piping after the MAF sensor. My flexible (or rather not flexible, brittle and dry rotted) rubber boot connecting the MAF pipe and pipe to the throttle body was cracked underneath letting in air past the MAF sensor.

I was luckily able to get a replacement at a toyota dealer since Lexus wanted $87 for it. After asking nicely, the parts guy dropped the price down from $55 to $35 for the rubber intake coupler. It's about an inch short but since its a bellow type coupler like stock, it's able to stretch a bit.

Part number I used was 17882-20161

 

Yeah that can cause problems, but I don't think (keyword) it would cause a cold idle problem, with lack of airflow past the mass sensor it would back off fuel delivery. So whats the news on it??????? Did you check for codes??