I have a 1.6L auto Lancer 2005. It was giving an unusual sound which upon checking turned out to be its timing bearing. When the mechanic replaced it, he told me that the tensioner spring bolt was broken and the spring was just hanging on. He told me that it would require an effort to remove the broken bolt so he just removed the spring and told me it would be fine. The unusual sound is gone and the car is running good.

What problem can removing this spring cause?

I have felt that the car is running on a greater RPM than usual. Is this because of the above problem or something else.

 

And this is why I don't take my car to shops......
God forbid someone puts some effort into their work.


Running at higher RPM is probably a vac leak somewhere, not timing related, however I would make sure you still have good tension on the belt. I would also extract that bolt and do it properly. Likely the "mechanic" broke the bolt replacing the belt and didn't feel like fixing it, so you should definitely deal with that as soon as you can.