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Alright before you do anything crazy, first remove the intake hose at the throttle body and use some brake clean or carb clean and get all the carbon build up off the butterfly valve out of there, (it could be holding your throttle valve open a pinch) After that if it still isn't better check the faults!!! We need fault codes in order to help you diagnose whats wrong with it. There is literally tons of things that can cause this, but start with the brake clean thing.

 

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Do a throttle body alignment. Disconnect the battery for 15 minutes.
Reconnect the battery and turn the key part way. Do not crank.
The throttle body will re-align in two minutes. Now start.

 

Yeah but dis-connecting the battery won't erase the throttle body alignment, its hard coded, but it couldn't hurt might as well do that too.

 

2000 has DBW.

 

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DBW - Drive By Wire,

what voltage is the alternator providing to the battery? a multi meter is required to check this,

never assume the battery is dead just because it is ( you should be asking why ) and in many cases its down to the alternator or internal parts like brushes/diode packs