I installed an aftermarket unit by Rostra in my 07 Corolla, but it's a
fly by wire throttle. I don't remember if they changed over to FBW in 04
or 05. If it's still the old style then you will need to install both
the controller and a separate throttle control unit under the hood.
With my 07 I only needed to install the inside unit---of course I did
have to cut a hole in the steering column cover for it to fit through,
but the connector and mounting holes were already installed. I just had
to connect it and attach the screws.
Google Rostra controls and see if their Corolla kit fits the 04 model.
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