Vacuum in the fuel tank: The vent tube is clogged. See if you can find it, a small metal tube facing down behind the rear wheel, under the fuel fill.
If fuel is leaking off the sprocket, you will for sure want to install a new IP belt, as the fuel deteriorates the belt. Also closely check the heater hoses in that area for deterioration.
If you can get some of the Volvo special tools, especially IP Pulley remover. P/N 9995204 21
Low-profile pulley remover will fit between IP and firewall
and
Lisle Shaft Type Seal Puller 58430
You should be able to R/R the shaft seal without removing the IP from the car.
See these other threads for more ideas:
IP air leak
Getting harder and harder to start
85 740 won't start