idling question
 

when the car is cold, the idling is high, up to 2800rpm. however, when it is warm up, the idling is back to normal. please let me know if you know what causing this. thanks in advance.

try removing the fast idle thermo valve and screwing the little white piece inside back in. I find it easier to just remove the whole throttle body and work on it like that, this way you don't actually have to take the FITV off the t/b. There are two little screws holding a brass plate on the fitv, remove this and it will expose the little white thing that i am talking about. Sometimes it backs itself out and causes a high idle.
Hope this helps.

how come only happen when engine is cold?

When you car is cold, your idle is controlled by the FAST IDLE VALVE. It has 2 coolant lines and 1 vac line going into it (I think).. Can't remeber exactly where it's located.. Depending on coolant temp, the fast idle valve will allow more air into the engine translating to higher rpm.

I would remove it and clean it out first.. If that doesn't help, replace it.

That will work! :D