Q: 2001 Mitsubishi Montero Sport running rough on idle

Take it back to whoever did that work--they did a crappy job. There are so many things that can go wrong. When you are changing all that stuff and replacing the timing belt off, odds are that the timing belt wasn’t put on and timed right. Those engines have overhead cams that are very hard to set.

If the mechanic didn’t have very special tools to hold those cams in place when he put the new belt on, a lot of times, they would move one tooth and one tooth is exactly what is going to make it run like that. Take it back and let them fix it or you can get your money back and go someplace else, because this is a very involved job and odds are there’s a tooth off on the timing belt. I see this all of the time. You can have this verified by having a technician, such as one from YourMechanic, inspect your engine’s rough idling issue before moving forward with a repair.