if the CD & Tape yield good sound when in use then it's the CDM box that is at fault. That box has a pre-amp that appears to be working if the CD & Tape work. The box also has all the radio functions, and the radio's tuner.
Unless the antenna jack has come out of the CDM box, and / or lost it's ground back at the mast location then the tuner sounds like it's out to lunch.
The CDM box is up under the knee bolster on the passenger side of the car. You have to take down that carpet panel, take off the door to the fuse box, and unplug 5 or 7 harness connectors that cross under the bracket that holds the box in place. To remove it is a real pia, it helps to remove the passenger seat so you have room to work. The bracket that holds the CDM is a twp piece set up that is fairly flexible plastic. The box has 5 or 6 plugs and two 10mm nuts that hold it in place. We may have a write up here somewhere.
Tom