Sounds like a relay in the fuse box. See my post here https://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=30988&p=141234&hilit=radio#p141234 where I had a similar problem. When I changed my faulty relay #105 with #106 in the diagram in that post, when the relay acted up, all my...

I have a '96 850r with a strange problem. I recently replaced the front O2 sensor after a sharp dive in fuel economy and trouble codes showing up. After driving around 150 miles and getting about 22 mpg in the city and 27 on the open road, I thought I was in the clear. However, as I was driving in h...