I have a 98 CRV with 130,000 miles. I don't drive this car too
frequently (about 100 miles one day a week). Took the car in for oil
change and the guy told me that it had lost 2 qt of oil since the the
last oil change (3,000 miles ago).

I have noticed that there was some black smoke coming out of the tail
pipe when I started my car in my every other week drive to my office.
I though that it was from the infrequent usage and the car was blowing
off the carbon.

I don't sense any lost of power of this 10 year old car.

What could go wrong and how do I do the diagnose? What is the cost of
respective repair?

I'd just like to educate myself before taking the car in.

Thanks.