Temp gauge problem after intake install

hi guy's i have a problem with my temp gauge after cobra intake install
i know that the stock guage is junk but do you know what can cuz a funny reading of the gauge i now that the car is not overheating (changed a sender unit for the gauge from ford) when the car starts to worm up seems to be good it goes to the m and r in 'normal' and then you can see that jumps to the L and back down and some times goes all the way to the H part and stays there
do you thing there is something wrong with the ground for the gauge that can cause this any body have a clue ??????
thank's
Derek.N

yes i did i used one of those pumps that sux all the air out the system and the hose's look flat and then i let the antifreeze back in and i got one of those t stats with a valve that should let air bubles out

Derek.N