2010 f150 4x4 makes a loud grinding noise only when turning left. It only happens when in 2wd. 4x4 functions fine and the noise goes away. I was thinking it might be the IWE Solenoid issue but my problem seems backwards, given that it works in 4wd but not in 2wd.

Suggestions?

 

If you are in 2wd and are losing vacuum, the IWE *WILL* grind. This sounds more like a problem with the IWE itself, not the solenoid. Troubleshoot the system using a handheld vacuum pump.