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My 1998 Hyundai Elantra 1.8L idles very high at startup. The colder it is outside the higher it idles. It does not have a tachometer but sounds like it is idling around 2500 to 3000 RPMs. Once it warms up, the idle will return to normal but sometimes I have to cut the air conditioner on to force the idle down to normal. This only works when the engine has ran for a few minutes and has warmed up. I even have to do this in the winter. I have replaced the MAF sensor due to a check engine code but this did not affect the idle issue.

Would removing the air intake between the mass airflow sensor and fuel rail and spraying intake cleaner in it while it is running possibly help? Could it be the air intake valve? I am trying to avoid removing any parts that have gaskets if possible.

Any ideas will help.
 

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Drives : Nissan NV200 Flies : Rans S6ES
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Could it be the air intake valve?
It sounds like the engine computer is incorrectly controlling the idle air control valve. The fact the idle speed returns to normal when the engine warms up suggests the valve itself is working. What you might try is clamp the long hose that links the idle control valve to the intake air duct and see what effect that has on the idle speed.

Since the problem is related to the temperature of the engine, you might also want to check the coolant temperature sensor. The temperature of the engine has a big effect on idle speed. If the temperature sensor output is incorrect so will the engine idle speed.

Regards.
Scottie.
 

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There are a few ways to test the temp sensor.

Monitoring the sensor output on your scan tool is probably the easiest way if your scan tool has that ability.
You could measure the sensor signal voltage by back probing the sensor signal wire on the harness connector.
Or you could measure the resistance of the sensor itself by connecting an ohmmeter across the sensor terminals (harness unplugged).

When the engine is cold the sensor signal voltage should be somewhere between approx 3V (at 20'C/68'F) and 4V (at 0'C/32'F).
Sensor resistance should be approx 5~6 kΩ at 0'C and will reduce as the temperature rises, reaching approx 2~3 kΩ at 20'C.
 
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