sixonemale

My '06 SC has about 72k miles and I've notice of late after starting it, it initially idles at about 1,200 RPM and tends to stay there until after driving and warmed up and then goes down. It used to start up at 1,200 RPM and after a very brief period of time would settle at 1,000 or 800 RPM, I can't recall exactly. My question is, is this normal related to the life of the engine, or do I have a sensor or other type of issue that can be addressed. My gut thought is that this is sensor issue, but am not sure which one to test or replace first.

Thanks in advance for any answers or thoughts.

Bgw70

It is not normal, I would first clean out the throttle body and run a code checker. If cleaning the TB and no codes are detected, I would then begins the process of looking a malfunctioning sensor...

I would also check for a vacuum leak...check vacuum hoses and idle air control...again could be carbon build up.

It will most likely be an easy fix.

sixonemale

Unfortunately no codes thrown. If you were going to look for a malfunctioning sensor, which ones would you target? I have not cleaned the TB yet.

Coleroad

When the engine is cold. The ecm is in open loop. It is not reading from all the sensors. Once the car is warmed up. It is in closed loop. It is now reading from all the sensors. Since the problem is solved by the car being warm. The computer reading from the sensors is able to compensate for the real issue. I would start with cleaning the throttlebody.like Bgw said a vacuum leak is a good possibility too.

sixonemale

I cleaned the throttle body, replaced the air filter and put some Sea Foam like gas treatment into the gas tank. It starts up at about 1,200 RPM when cold and when warmed up it idles at about 920 RPM in park and in drive when stopped it idles at about 600 RPM. The throttle body looked pretty clean. I'll know if any of this had any effect tomorrow morning.

sixonemale

No luck, the car starts up at around 1,200 RPM and does not want to go down with the press of the gas pedal after 30 seconds of idling. Does anyone have any thoughts on which sensor could be the culprit? Also, with no check engine lights on, would a good OBD II code reader find the sensor? Thanks in advance for all replies.

Bgw70

Check for a Vacuum leak and idle air control valve.

Google the how to check these items and watch some YouTube videos...

Coleroad

+1 -----------

sixonemale

Thanks,. the idle air control valve makes a lot sense at what to look at or replace first. I did check for a vacuum leak yesterday and could not find one, but I may have a mechanic do that.

Coleroad

Smoke test is the only viable way to find a small vacuum leak. You could spend hours trying to find it otherwise. If you don't mind, how did you go about cleaning the throttle body?

sixonemale

I took off the air hose attached to the throttle body and inspected it first and it looked very clean, no visible dark deposits of any kind. I then sprayed cleaner, specifically for cleaning the throttle body, with both the choke plate opened and closed.

Because I could not solve the problem, I took the car to a Lexus dealership and they spent one hour of time and told me there is nothing wrong with the car. I could not disagree more, I know how these cars idle when started up. Something is wrong, but they simply cannot detect it, frustrating. What I don't like about the conclusion of this dealership is that I know how the car is suppose to run and verified it with another owner over the phone, but because the computer reading say it's okay, they believe it vs having very experienced mechanics who could recognize this malfunction.

Coleroad

Here is a decent video for cleaning the idle air control.

sixonemale

Thanks for video. I owned another car that had a rough idle and did exactly what that video showed and it did smooth out the idle. Unfortunately I do not think it is the idle air control valve, the idle is very smooth, not rough at all, just stuck at high RPM's. Typically when the car is started on a cold day the idle used to drop down fairly quickly or did so by tapping on the gas pedal, now it won't. I think it's sensor going bad.