IronX is your friend in this scenario - Tardis will only remove tar, not brake dusting pitting which is what you are seeing.

IronX in action:

http://www.flickr.com/photos/42262279@N04/6786425618/http://www.flickr.com/photos/42262279@N04/6786425618/ by http://www.flickr.com/people/42262279@N04/, on Flickr