870 Egr fault 2357 Mechanical

[Andre_The_Giant]

I have a mandated 870 that just started getting an EGR fault 2357. (Mechanical system not responding or out of adjustment). The light comes on very rarely, and only at an idle. I plan to follow the repair procedure this weekend. But I noticed that when the code is active, my logged Turbocharger speed jumps from 20,000rpm to 3,000 to 0? It only does this when egr is closed.. The truck has been having minor strange boost spikes and boost drops from time to time too, would a malfunctioning egr cause this? Sorry if this is a stupid question, I’m new to Insite and all of the parameter values