sixonemale

When starting your SC on let's say a day where the temperature is 35 - 55 degrees, what is your initial idle RPM?

Next, how long does it take to settle down to a lower RPM and what is lower RPM when the car is still in Park?

Lastly, can tapping the gas pedal after initial start-up bring the idle RPM down while the car is in Park?

Thanks in advance for these answers.

sixonemale

What I'm really asking here is does your initial idle of about 1,200 RPM drop down within 30 seconds or so? From what I remember it does drop down and now my idle is not dropping down until after the car is driven.

Harold57

We haven't really seen temperatures low enough to test here in the Dallas area yet but generally, it will drop down within 30 s or so as you mentioned.

Othic

Itll say higher longer when its cold. Its for emission purposes. Per TIS Standard idle speed: 700 to 800 rpm. That's warmed up of course.

Bgw70

Do you have any issues when the car is warmed up?
When did problem begin to happen?
Was it all at once or did it gradually show up?
Does the outside temp determine how long you have a high idle?

I may be wrong but tapping the gas to lower the idle applied to carbureted engines with electric or exhaust heated chokes. If the choke spring was warmed enough, you could tap the accelerator and it would release the fast idle cam.

Coleroad

Right on the mark, bgw70.

Bgw70

Why thank you Cole ;-)

I am finding it difficult to narrow down the problem with these symptoms. He may not have a problem If the engine is idling high for a longer period of time and the temperature is much cooler.

sixonemale

I can't say for sure when the problem began to happen, but probably over the past couple of months, my wife the drives the SC regularly, me only occasionally to make sure it's running properly. Because I don't drive it regularly I'm not sure if it was gradual or showed up at once, but it did take a turn. I put the temperatures down because I thought maybe the ambient air temperature had something do with it, but it does not, especially in the warm climate that we live in.

Most importantly I have confirmed with two other long term owners from this board and yes the idle does drop pretty quickly as I recalled.

Bottom-line something has changed. I cleaned the MAF, throttle body. Something has changed and my guess is that a sensor is slowly going bad.

Coleroad

The only sensors that to me makes sense that it could possibly cause this condition is coolant temperature, intake temperature.

Coleroad

The same question was asked only a couple weeks ago. I'm with Bgw on I think a small vacuum leak, or the idle air control. A air leak in the intake any where after the maf sensor can also cause this.

sixonemale

You may have missed a post, a Lexus dealership analyzed it and could not find anything wrong with it, like a vacuum leak, etc. It's simply unfortunate they do not know how this car should start up, perhaps the SC is somewhat forgotten by them, in that less exist and are worked on less often.

I also think there are more sensors that could be causing this that could be going bad besides ECT and air intake sensor. I don't think it has anything to do with the coolant temperature. Coolant takes awhile to warm up and flow, long after the idles comes down.

Bgw70

We are only trying to help you and give you things to check.

Here is a $5 item you could try, have you ever changed the PCV?

I don't remember how miles are on your car but this is one of these over looked items.

BTW, I certainly pay attention to what what Cole writes, he knows cars.

Okay, back to your problem.

Give us refresher of what you have done and any parts you changed so far.
You already said the car was checked out by a mechanic and they found no vacuum leak.

A few days ago, Cole asked you how you cleaned the throttle body, did you answer him? I cannot remember :-)
Did you take any pictures of the cleaned throttle body?

Next time you start it cold, please let us know how long it takes before the idle is at 800-900RPMs unless you already know...here is a thread on this subject.
Cold start thread
In general, Toyotas will start the same.

Coleroad

If the coolant temperature sensor is telling the computer the engine is warmer than it is. It is not running rich enough and would therefore have to idle faster to keep the engine running till it did reach operating temperature.

Coleroad

There are only a few sensors that will affect the idle speed while in open loop. If it was like the throttle position sensor it would affect it both cold or warm. It's these things I'm taking into account when talking about possible solutions. Something else that comes to mind. When was the battery last replCed? Even though it starts the car fine it can still be weak enough to cause all kinds of funky problems. Running ruff, all kinds of cel's, gauges going wonky, just things that can have you chasing your tail. I personally would pull the plenum between the maf sensor and the throttlebody. Look for any kind of crack in it especially in the accordion part of it. You would be surprised at how a small tight crack in that can cause problems. It can look like such a tight crack that you would think no air would pass through it.

sixonemale

My SC has about 72k miles on it and I have never cleaned or changed the PCV valve. The throttle body was spotless, but I cleaned it anyway and also cleaned the MAF. I also inspected for vacuum leaks and one other mechanic look for them, in addition to Lexus running the engine on the computer and finding no leaks or anything wrong. Cole does shed some good light on the ECT, which I may replace along with the PCV valve. When buying sensors I tend to only use OEM due to poor experiences on other cars using aftermarket sensors. The battery is not that old, but I hear what you are saying about what a bad battery could do, but I don't think it's part of the problem at this point and time.

As of now it would take a long time for the idle to get to 800 or 900 RPM in park, it's much easier for my wife to run the car to get the idle down. Bgw, the link that you supplied is spot on with regard to how it should start up and drop down to 8-900 RPM in about 30 seconds. It's still beyond my wildest imagination that Lexus would or could say everything is okay.

I will take a look at the plenum for a leak and will probably replace the PCV and ECT sensor, it's a low cost attempt to fix it.

Thanks for the thoughts and ideas.