Air Injection Reactor.... That's the air pump pushing "fresh" (cooler) air into the exhaust system at the valve, "continuing" the burn as the spent mixture goes through the exhaust system. This significantly reduces emmissions. There's a slight parasitic loss from the pump, but performance "loss" is grossly exagerated by "lore". In fact, one can use the pump to their advantage. Small block Chevy in particular, uses tubes that are long and inject the air right near the valve itself. When installing headers in California "back in the day", we had to adhere to rules regarding disabling any emmission control. Can't do it. So we bent the tubes in a "curl", so they'd go down the header tube instead of into the port. The result was a slight gain in scavenging by creating a lower pressure in the pipe than the chamber/port. And all still passing "smog".
Usually, a failed pump is locked up. Sometimes they'll squeal prior. A blubbering sound can also indicate a problem.