I believe you are always supposed to have the presser foot down when free motion quilting; otherwise, the upper tension discs are not engaged.
I would experiment with the upper tension only first. Instead of loosening it, I would tighten it and see what happens.
Most people lower the feed dogs for FMQ, but some find it easier to FMQ with the feed dogs up. Just make sure, if the feed dogs are up, that your stitch length is set to 0.