where is it located on a 88 jag 3.6? what is its function? is there a way to diagnose it, and what are the symptoms of a bad one? just out of curiosity.. thanks in advance

 

Technically, not sure if it's the same on Jags, but on BMWs air pump check valve is a fancy name for egr valve and its function is for emissions. The air pump pipes fresh air on cold starts to reduce emissions. In reality it makes for dirty intake ports and waste engine bay space.