1984 White, 1997 Silver. Drive it like you test it
You would need a scanner to enable the air pump and check few things to make a full diagnostic. However, due to corrosion and carbon built up the valve is the culprit most of the time.
Check for any hoses and pipes for being connected, clamps secure on pipe and hoses, no kinks, hole or pinches hoses. You can replace the check valve. This is less that $50 if I recall correctly. You just need to remove the clamp from the rubber hose and disconnect the valve from the air tube. The valve is on the driver side of the engine as you can see on picture. The valve is the black think that looks like an UFO between metal air pipe and rubber hose. The green <R> of "Remove air Pipe" touches the valve.
picture from DIY spark plug change, but that will give you an idea.