95 Ls400 Fast Cold Idle

[Patric]

I've done a search and can't find any info on my problem.

Starting the car up cold each day the idle is between 1800 and 2000 rpm. This has been slowly going up the last few years.

As the engine warms it slowly decreases to 750 rpm at normal operating temp.

I have had the car to TWO Lexus dealers who have checked the car and say everything is operating normally. B.S. They say there is no idle adjustment on this car. Idle is controlled by the PCM with input from the various sensors which are all working normally.

This has been a great car for me but I'm about at the end of my rope and am considering getting rid of it for the above reason.

Anybody have any ideas? Is it time to move on?

Thanks;

Pat

[dfkd]

This is absolutely normal.

Every fuel injected car I've owned (even the crappy Ford Taurus) has done that.

From what I've read, the engine computer does that when the engine is cold to reduce the amount of bad emissions until the car is at normal running temperature. It has to do with heating up the cat converter quickly because it works most effectively when hot. It's good old chemical thermodynamics. Higher temperature = more effective reaction. Combine that with the fact that at cold start the car outputs its worst pollutant levels and it makes sense to heat it quickly.

Under normal operating conditions, the catalytic process doesn't begin until temperatures inside a converter reach 500 to 600 degrees (F). If air/fuel ratio is on target, and the exhaust is free of contaminants, internal converter temperature stays at about 1200 degrees.

This warm-up period immediately after a vehicle is started is when the catalytic converter is least efficient and the vehicle expels the most pollutants. Some vehicles employ a pre-converter in the exhaust system immediately after the manifold to help during this warm-up period. The pre-converter's small size and proximity to the engine allow it to heat up and start functioning in less time than the main converter. It also pre-heats the exhaust gasses and helps the main converter reach operating temperature sooner

Also, remember the old days or carbs when you'd have to pull the choke to cold start a car? In today's world, the car does it for you.

[LScott400]

Service Manual says:

IAC Valve Circuit Circuit Description:

The IAC valve is provided on the intake air chamber

and intake air bypassing the throttle valve is directed to

the IAC valve through a hose.

A step motor is built into the IAC valve. It consists of four

coils, the magnetic rotor, valve shaft and valve.

When current flows to the coils due to signals from the

ECM, the rotor turns and moves the valve shaft forward

or backward, changing the clearance between the

valve and the valve seat.

In this way the intake air volume bypassing the throttle

valve is regulated, controlling the engine speed.

There are 125 possible positions to which the valve can

be opened.

Perhaps it needs to be cleaned/inspected?

[dfkd]

Service Manual says:

IAC Valve Circuit Circuit Description:

The IAC valve is provided on the intake air chamber

and intake air bypassing the throttle valve is directed to

the IAC valve through a hose.

A step motor is built into the IAC valve. It consists of four

coils, the magnetic rotor, valve shaft and valve.

When current flows to the coils due to signals from the

ECM, the rotor turns and moves the valve shaft forward

or backward, changing the clearance between the

valve and the valve seat.

In this way the intake air volume bypassing the throttle

valve is regulated, controlling the engine speed.

There are 125 possible positions to which the valve can

be opened.

Perhaps it needs to be cleaned/inspected?

If this were the case the car would idle too fast all the time, regardless of its "warmness".

[Patric]

Thanks for the info guys.

When I bought the car 7 years ago the cold idle was around 1200 depending on the ambient air temp. As stated, its been going up slowly the last few years to where I don't have any reason to expect it will stop and may well be 2500 before long. I'm wondering if the dealers will still be telling me its "normal" then?

Too bad it doesn't have a simple idle screw like the old carburated cars had.

Pat