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P0456 and High Engine Idle

Hi guys, recently my 2005 scion tc CEL light came on and I diagnosed p0456. At the same time when I turn the car on in the morning it idles at 2k RPM for about 3 minutes and then the idle goes down to around 900. If I park and return to the car within 2 hours the idle stays down but if I wait it goes back to 2k and I have to wait a few minutes for it to come down. My question is whether this is related to p0456 and any suggestions as to what could be wrong and how do I fix it?

Thanks guys

The DTC P0456 indicates a small leak in the EVAP system. This can be caused by something as simple as a loose gas cap. But this wouldn’t cause the fast idle.

The idle is controlled by the computer on a cold start by the signal it receives from the coolant temperature sensor.

The first thing to check is make sure that the coolant is at the proper level. If the coolant is low, and air comes in contact with coolant temp sensor, it’ll send a false signal to the computer causing it to think that coolant is really cold, causing the high idle.

If the coolant level is fine, then the problem might be with a flaky coolant temp sensor for the computer.


I’m going to go against the grain here . . .

I’ve had many toyotas over the years, and all of them have had a high idle for a few minutes, if I was starting the engine stone cold. From day one

In fact, my daily driver is a 2005 Camry, and it does exactly that. Trust me when I say there’s nothing wrong with my car, in regards to the high idle

Not related to P0456, in my opinion