Fuel Gauge stuck & unresponsive
 

96 Saab 900 S 2.3 liter that has 165K on it. For quite awhile now the fuel gauge indicator would get stuck at the full tank side of the indicator and then out of the blue it would drop down to it's actual tank contents (I.E. half of tank) but then it would go back up to full for no apparent reason while driving. This was just annoying and incovenient but now the indicator seems to be stuck at the full and won't even drop down to it's actual reading. Anyone have an idea as to what is causing this, and how much the repair might run me?