gas guage is reading wrong

03' neon....what could cause my gas guage to read wrong...like when i fill up my car it won't reach all the way to Full..it plays around with u ..say when car is in motion it will drop alil ..but when u turn it off n on u will no where the right reading is at..when in motion again it will drop alil again.... what could be the problem ?.

Fuel sending unit may be going bad on you.

How many miles are on the car? If its gone past 150,000 miles, you might want to start budgeting for a new fuel pump/pickup/sender unit. (Its often sold as one assembly, an expensive one) They dont last forever, and its a LOT more convenient to get it replaced before it quits. I.E. you can drive the car to get it fixed instead of having it towed in. "Pre-emptive repair".

the car has 130,000 miles on it , i kinna knew that woulda been the problem to....fuel pump.