I have a 2008 Toyota matrix automatic drive with 95000 miles. The fuel guage indicator on the dashboard moves little up and down at different instances. It could be at a particular mark at the traffic lights and then moves down whilst moving. How do fix it. By the way I have replaced the sender unit twice but to no avail.
It sounds like your fuel gauge is functioning normally. If the float to your sender is toward the front of the gas tank, it's going to go down as you take off forward because the liquid will shift to the rear as you move forward and measure a lower level. The true reading should observed while the car is still and level. You will also get a different reading if going up a hill, going down a hill or making a sharp turn. Gauge movement might not be as obvious on other cars because the tank has baffles in it and/or the indicator is slow to respond by design.
From personal experience, I had a gas gauge needle that wouldn't go all the way to F for full even after filling the tank all the way up. Turned out to be a loose ground wire. Tighted a screw terminal from the instrument cluster wire to the dash frame, fixed.
Thanks a lot.