Problems Using Stud Finder on a Textured Wall - Due to Finder or Texture?
I haven't tried it on a textured wall, but have similar issues with uneven plaster and lath. Try maintaining a steady speed and pressure on the stud finder as you sweep across the wall.  (I'm much more steady with my right hand than my left.)  Try going both directions - left to right, and right to left - at several different heights. Most walls have light switch or outlet boxes attached to studs. Once you find a stud, try searching 16" or 24" to the side.  (Most walls in the US are framed 16" on center.)  It helps to put a strip of painter's tape 8-12" long where you think a stud is, then make repeated passes back and forth, marking the edges each time with a pencil. With some practice (and a bit of luck) you'll find your marks in clusters on each stud edge.  Once you find a couple studs on that wall you can measure and put another piece of tape to use as a starting point for finding others.