If you notice a corkscrew type of arrow flight your idler is probably not vertical at full draw. I'm not talking about fishtailing or porposing. It is exactly that a corkscrew type of flight. If your arrow flight looks good , you don't have a lean problem.
Make sure that your axle to axle measures the same on both sides of your bow. This will usually put the idler in the proper position. At full draw have someone stand behind you and look at the position of the idler. It should be striaght up and down. If not , twist the buss accordingly.