would a vane air flow sensor be responsible for idle levels to drop around 500rpm and if so would replacing the sensor fix the problem? Or can there be anything else that might be affecting the idle levels? Btw the car is a 90 FC

any help would be appreciated!

 

A bad AFM can cause a poor idle or stalling, but so can vacuum leaks or a bad/non-adjusted TPS. You can pull engine codes while you're at it to see if anything has failed: http://www.johnr.com/cpucodes.html.