2002 Mitsubishi Galant stallng

Hi jpitt2k2. Welcome to the forum. If this started right after you disconnected the battery to replace the starter or generator, the Engine Computer likely lost its memory and "minimum throttle" will have to be relearned before the computer will know when it has to be in control of idle speed. I only know how to do that on Chrysler products, but they use a lot of Mitsubishi parts so the procedure might be the same. Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. The high manifold vacuum for seven seconds is the signal for the computer to memorize the voltage coming from the throttle position sensor, and the computer knows your foot is off the pedal and you are coasting. From then on, whenever it sees the same voltage from the throttle position sensor, it will adjust idle speed automatically.

Caradiodoc

Just so I'm clear, the engine only stalls when you come to a stop and it will always restart, is that correct? If you mean it stops running while you're cruising at a steady speed, that's a different symptom.

You're right about losing its memory. A lot more is lost than minimum throttle, but that's the one you will notice until it is relearned. Short and long-term fuel trims are also lost. What is not lost from memory are the factory-pre-programmed fuel delivery values for every possible operating condition. As you drive, the computer starts with those values, then watches the readings from the oxygen sensor(s). Based on those readings, the computer will add or subtract a little fuel from the pre-programmed amount until it reaches the perfect mixture for every condition. That's the short-term fuel trim. When the computer sees the same modifications being made over and over, it uses those new updated values as the long-term fuel trim and will start running on those values immediately after startup. That results in lower emissions and better performance all the time. When the battery is disconnected or run dead, those fuel trims are lost, but normally they are relearned so quickly, you don't have time to notice a loss of performance.

On most cars, customer preferences that are programmed in to a computer are remembered when the battery is disconnected. Such things as speed-sensitive door locks turned on or off, a horn chirp when the doors are locked, and things like that are usually retained, but one notorious exception is with Volkswagens. They will not come out of park and the engine will not increase above idle until minimum throttle is relearned after the battery is disconnected or run dead. To do that requires the vehicle to be towed to the dealership when they are open. Typical repair bill for running the battery dead can run over $1000.00. Got'cha!

Caradiodoc