From what I've read some say a small line (1/8") will stop the fluttering and others say a 1/4" worked for them.
I've got 3/16" or 1/4"(can't remember at the moment) and mine fluttered really bad when I first installed it. I took a pair of pliers to collapse the line and that helped calm the gauge down but not enough so I'm going to try the 1/8" line I bought. I also think I've got to much copper line so I was going to first remove some and try that; then install the 1/8" line.
I could be wrong though, it's known to happen.
Yellowchevy