Do not change the rod length. Yes, some will say that you can dial your car in by doing this. I fooled with it years ago, same with adding and removing shims on barometric cell. But ultimately, I put it all back to stock. Something else is wrong. Read edmayos post to get you started..
https://www.early911sregistry.org/forums/showthread.php?48679-MFI-rod-lenghts