Q: Lower idler pulley

Hi. No, you do not need to replace the bolt when changing the idler pulley. You must be very careful not to over torque the bolt or this will cause damage to the treads which in turn may allow the bolt to come loose. Remove the bolt and inspect both the bolt threads and bolt hole threads. If all of it checks good, you can apply a drop of blue lactate to the bolt and torque the bolt to spec. If damage has occurred to either bolt or mounting surface you will need to replace the damaged part. If you would like to have this taken care of for you, a certified professional from YourMechanic can come to your car’s location to replace the idler pulley.