1984 volvo 760 turbo sputter & wants to die when slowing down or stopped

Lately my car has been wanting to die when slowing down or stopped. Runs great on freeway. RPM's won't stay above 10 in drive, but will stay above in all other gears. The only way to make the car run right is to have the dial set to Auto on the air/ac/temp/ setting. when you do that the gas gauge goes down. If you slide the knob back to lo or off the car wants to die, and the gas gauge goes back up. The turbo gauge on the dash does,'t move so I don't know if it works.I don't know if that makes a difference. Changed fuel filter, no change . Also I have been smelling fumes. It's been like this for about a week, but has got worse. Checked vacumne hoses and replaced a few. Thanks