Q: Car only starts when I pump the gas pedal.

From this description it seems that there could be separate issues happening to your Mitsubishi Eclipse. The three most common reasons I see for a car unable to start without pushing the gas pedal include; the throttle body gasket may have been installed incorrectly, the idle speed control screw needs to be adjusted and finally the throttle position sensor may need to be adjusted.

Every car may be made up of the same parts but they all install and work slightly differently. Sometimes parts aren’t ready to install right out of the box so it is necessary to make certain vital adjustments to the part, in order to have the throttle body do its job properly. If this is the case, a trained professional can easily diagnose this concern on your car and determine if this is indeed the problem and will be able to make the adjustments necessary. While they are doing this, they can also inspect the idle speed control screw. The engine will need to be running, allowing the screw to be adjusted to run at the specified RPMs for that vehicle. Finally, with the throttle position sensor, a certified mechanic can adjust it by using the manufacture specs, it needs to be installed and clocked (turned a specific way) then a voltage meter is used to check the signal voltage (signal voltage is 5v and as you step on the gas pedal the voltage will vary from 1.5 up to 4.5 volts to tell the computer where the position of the throttle is and use his information along with other sensors to determine how much air and fuel are put in the engine) to ensure that the voltage specs are in the proper range.

As you can see, it is important to have a certified mechanic to look over this problem so they can diagnose which part may be failing and get you back on the road safely.