Engine acting up after adding motor oil Options

[DaijoubuDa]

I checked the oil level a few days ago and it was really low. It was the first time I added oil since I bought the car last month, and I have no idea which type of oil the previous owner used. So, I just added about a quart of Castrol GTX 10W-30 High mileage motor oil to bring it up to the halfway point between low and high marks on the dipstick.

Since then, my engine (7afe) had been acting up. For instance, the engine sometimes vibrates very roughly when I stop at the traffic light or driving on highway; engine sometimes get really noise; and the car feels sluggish sometimes. (Symptoms are more noticeable after driving for awhile. Not with cold engine)

So, I am just wondering if this is normal or maybe something is wrong with the engine?

Note: Do you think it has anything to do with the catalyst converter? Last month, I was told that there was a small leak on the catalyst converter and I will need to get it replaced eventually.

This post has been edited by DaijoubuDa: Oct 31, 2013 - 6:34 AM