When I rev the engine and hold it at a constant 3K rpm, the idle will consistently drop a couple hundred and then go back up to 3K rpm ... which the drop happens, the A/F gauge bounces from rich to lean and then back.

The 2 things happen in perfect unison.

 

misfire?

 

Vacumm leak.

 

would it do this if a intake manifold was leaking?

 

ttt