1998 Volvo S70

The first thing you should do is inspect all the vacuum hoses to the air injection, especially the one to the diverter valve. They get very soft that they collapse causing a restriction or a leak. The majority of the time, that is all I have had to fix. Sometimes it does get a little more complicated then that but replacing the rubber vacuum lines should be your first an cheapest step to start with. You can buy the hoses from Volvo and recommend it since they are already shaped and formed to fit on there. You dont need to replace the plastic lines, just the rubber ones and they are sold separate. Also replace the rubber hoses on the vacuum solenoid valve also near the radiator fan as well since they get really soft and brittle also.