High Idle speed after driving

[NICAT]

Hi.
Starting the engine, Everything is fine. RPM rise to 2000 once started, stays there for two or three seconds, then little by litlle it goes down to 700RPM. So far so good.
Driving car for a while (May be 10 - 20 minutes), then the idle speed is 1500 but not less. I wait for a while, but it does not goes down. Turning off the engine, an start it again immediately, idle is 700 RPM again.
Pressed gas pedal several times to make sure that idle air control valve is not stucking, but it again goes down to 700RPM.
What could be the reason for high speed idle after driving ?
Check engine light does not flash at that time.
Daewoo Nexia 2006, G15MF engine.
Regards

 

[StevieC]

What's the mileage and are they original 02 sensors on the Catalytic? I had a bad 02 sensor that was keeping my idle high because the ECM thought the catalytic converter was falling in temperature.

 

[NICAT]

Ah, there is no catalytic converter
PS: Milage is something more than 1 Million KM, But engine has been rebuilt recently by replacing almost every single part. It is in its 20.000km after rebuilt.

 

[StevieC]

Do you have access to a scan tool that you can read the sensors live data with?

 

[gathermewool]

You said the check engine light does not flash at that time. Does it flash at other times?

Is the check engine light on (and not flashing) at other times? What are the codes?

 

[NICAT]

Sorry for poor english. Check engine light never flashes

Check engine light is never on.
A year ago car's throttle position sensor was bad, at that time the idle speed was also very high (about 3500-4000rpm) and check engine light was.
Unfortunately the information we can get from the car by a scan tool is very limited. But still i will try to have it scanned tomorrow and update here.
Thanks

 

[NICAT]

A year ago, car's idle was 4000RPM, No mechanic could find the reason in the city.
Then the only creative solution they offered me was removing idle air control valve cable, Manually adjusting the pintle position, and adding some glue to fix it there.
Then i found out that a cable of throttle position sensor is bad.
I hope to find better solution this time

 

[zorobabel]

I had a similar problem when outside temperatures were lower. It was a stuck open thermostat.

 

[mk378]

A very common reason to idle too fast is that the throttle cable or plate is sticky and doesn't close fully when you stop pressing the gas pedal.

Originally Posted by NICAT
A year ago, car's idle was 4000RPM, No mechanic could find the reason in the city.
Then the only creative solution they offered me was removing idle air control valve cable, Manually adjusting the pintle position, and adding some glue to fix it there.
Then i found out that a cable of throttle position sensor is bad.
I hope to find better solution this time

If it is not set up as stock now, you would have to remove all those mods first. It's not going to idle properly without an air control valve.

 

[NICAT]

Originally Posted by mk378
A very common reason to idle too fast is that the throttle cable or plate is sticky and doesn't close fully when you stop pressing the gas pedal.

Originally Posted by NICAT
A year ago, car's idle was 4000RPM, No mechanic could find the reason in the city.
Then the only creative solution they offered me was removing idle air control valve cable, Manually adjusting the pintle position, and adding some glue to fix it there.
Then i found out that a cable of throttle position sensor is bad.
I hope to find better solution this time

If it is not set up as stock now, you would have to remove all those mods first. It's not going to idle properly without an air control valve.


You are right, It was not idling properly with that mod. At cold start i had to press on the gas to prevent engine from turning off.
But later we had fixed it

 

[The_Jeff]

Easily your throttle position sensor.

When you start the car, it checks its voltage for a "closed reference". Say it's .40 volts. Later in that run cycle the TPS gets flaky and reports .42 volts at idle. Car thinks it's not at idle and needs to "dashpot" and opens the idle air bypass all the way. Does not throw a code because .42 is a plausible reading.

Turn car off, turn it on, .42 is the new idle baseline and it shoots for 700 RPM, the hot idle speed.

 

[Rand]

you need a scantool that can see live data. There are bluetooth devices 10-15$ on ebay or amazon.. use with android phone and torque app.

a regular "code scan" will show nothing probably.

Seeing O2 sensor data etc will be more helpful to diagnose.