I'm wondering if it is the most common type of Mitsubishi engine the 4G63 1970cc engine? If so try changing the fuel filter first. Then if your have been running on fuel with alcohol added then try not having any alcohol and use a higher octane fuel. If you have a catalytic converter on you exhaust then remember it must be unleaded. The recommendation for similar faults also includes changing the air filter. If it if fuel injected? Check the MAF sensor? but that if not my vehicle so you will have to look that up.