Here is how I would start
Remove and clean the terminals from your battery, with wire-brush, Emery cloth, and/or Industrial-Level 3M Scour Pad.
Remove, clean, and tighten the grounds in/around the engine bay.
- Leave the Battery Terminals disconnected.
- Ensure all electrical items are off (headlights, HVAC etc etc)
- Connect your Battery terminals.
Be prepared to sit in the car for over 20 minutes! Have a watch/clock.
Get in the car and close the door.
- Put the key in the ignition, but don't turn it. Wait 30 seconds.
- Turn the key to ON, not START. Wait 1 minute.
- Start the car, Wait 10 minutes. Yes, 10 minutes. DO NOT touch the gas pedal, brake pedal, or anything for the ENTIRE time.
- After running the engine, without any input for 10 minutes. Turn the key to ACC/OFF. Wait 30 seconds. You should hear a Relay click off.
- Remove the key. Open the door wait a second, close the door. You should hear a relay click off within a minute. If not simply proceed.
- Key in, wait 30 seconds.
- Key to on wait 1 minute.
- Key to start wait 10 minutes.
This is an amalgamation of numerous manufacturers Idle Relearn Procedures. This seems to cover all the bases, regardless of the car. If you're not happy with the times, please look up Mitsubishi's actual Idle Relearn Procedure, though it's likely to be very similar to this.
Cleaning and tightening your battery terminals and grounds is simply good maintenance, if nothing else. Generally a corroded ground can cause all kinds of issues. This is a quick and easy way to ensure clean power, and rule out issues there.
The Idle relearn procedure is going to do two things in this case. One it will allow the vehicle to find baseline idle again, since the battery was disconnected. The other benefit is that if there are any issues which will set a code, they will likely show up. I've had numerous cars with symptoms that did not "throw" a code until a battery reset.
If the battery is disconnected, but the vehicle does not have the time to form a baseline-idle, numerous issues will occur like stalling/stall-like conditions. The vehicle will eventually learn baseline, but it will take far longer, with far more issues than simply performing the "Relearn Procedure".
These procedures will result in one of three things:
- No change.
- Code Set.
- Issue Resolved.
If the result is 2, have the code(s) read at a local Autoparts Store, or use a ODBII reader, etc.
If the result is 1. then I would further diagnose Fuel, Spark, and Air. Ensure that the Fuel Pressure Regulator isn't leaking, Check Fuel pressure at the rail with the engine on and off. Ensure that all your Plug Tube Seals are good, that plugs are not fouling with oil, etc. Ensure that your air filter is clean, air box clear and clean, MAF is clean.
Ensure all Fluids are present and correct, especially coolant and transmission fluids.
If all of these check out, I would check the O2 Sensors with a multimeter/Scan Tool to ensure that they are operating within proper range.
That is where I would start.
I hope this helps.