1998 Volvo S70 Engine Stalls

I have a 1998 Volvo S70 Turbo that trys to stall while idling. If I push in on the clutch the rpms jump back up to normal 1k or so and its fine. I have notice a smell also coming from the exhaust (strong sulfur smell which is not normal). When the idle drops low the check engine light will evently come on. I checked the DIL with a code reader and it s reading a PO171 lean fuel mixture Bank 1. When I clear the code the problem goes away for around 500 miles but will evently come back as before with the low idle and a stall when sitting still. It will start up after it stalls but I can see the tach needle drop as before. Pushing in on the cltch while sitting still make the proble go away. I'd hate to keep having to push the clutch in while still. Cluch job is in the couple thousand price range.

Any ideas.....Thanks