Starts but won't idle - 2001 Mitsubishi Eclipse

change the fuel filter and check the fuel pressure

are there any codes? sounds to be a bad idle air control valve

not specific enough, what kind of car? Year? Make and model could be multiple reasons for these symptoms. Could be something simple that needs service such as the Idle Air Control Valve

has base idle speed and kurb idle speed. allows engine to close throttle opening when shutting down to stop pre-ignition or engine running on

An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or PCM (powertrain control module) receives information from various sensors and will output signals to adjust the idle air control motor in or out to adjust engine idle speed by controlling engine idle air. An idle air control motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the idle air control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak idle air control motor.

If it starts and runs, but won't idle, could be a vac leak, dirty throttle body, or faulty idle air control valve.

If it starts and idles about 2000 to 2500 rpm and won't slow down about 90% of the time replace idle up motor(sensor)

It may be your distributor if it seizes up when it is hot it won't idle.

Sounds like the Throttle Position sensor or the Idle Air Control Valve causing the issue