A common cause of engine racing instead of idling is the failure of the idle air control motor. You can find it by following the air hose from the air intake/air filter box. There is a short connection to the air mass meter (AMM) aka mass airflow sensor (MAS) and then a pleated hose into the throttle body.

When the throttle is closed, no air gets into the engine, so it dies. Except for the idla air control motor. There are two air hoses that come out of that pleated air hose just before it connects to the throttle body. One is on the firewall side and goes to the PCV system, the other is on the radiator side and goes to the idle air control motor, aka IAC.

With the engine running when it's supposed to be idling, use a pair of pliers to close off that hose to the IAC. If the idle drops down, the IAC has a problem. It may mean that the throttle body is so crudded up that the throttle position switch, which tells the computer to operate the IAC, never trips. It could be that the wiring harness had crumbling insulation and the signal wither never gets to the computer or never gets from the computer to the IAC.

The IAC can be burned out or just gunked up and stuck. 17 year old cars have problems, y'know. With the key off, disconnect the wiring harness and check between the IAC terminals with an ohmmeter. There should be resistance between each pair, the Haynes manual will give you specs. USe the resistance test on any IAC you get from a salvage yard. The part numbers MUST match.

AND, get another mechanic.

Good Luck,.

Bob

:>)