I was leaving work today and started my evo 8 up like normal to head home; wideband showed normal 14-16 afr for the first 5 minutes of (non spirited) driving. After that, it started getting really rich, dropping from normal to 13, 12, 11 and held between 10.5 and 11 between 50 - 60mph with no boost whatsoever. When I came to a stop it nearly killed and it reeked of fuel. Check engine light kicked on... I didn't have my evo scan with me so I couldn't check what it was but I just wanted to see if anyone could give me a couple quick ideas on what the potential cause is. I was thinking a faulty fuel pressure regulator. Any help?

 

that's a big change...I would start with a boost leak test just to eliminate that but it would have to be a massive leak...