ISX 12 spooling at idle

[JimT]

Do you have Insite? Pull up Data Monitor and watch different params. See what, if anything changes at the same time. Simply unplugging the EGR doesn't really narrow it down, although a full EGR Tune-up would probably be a good place to start. Clean out everything, including the EGR valve. While it's off gently and carefully check the spring loaded butterfly valve. Watch your fingers, but make sure it can open with some pressure and will spring back to closed after. Don't try to force it if it doesn't want to move, mainly because you don't want to get hurt.

The turbo is used for multiple applications on these emissions trucks. From SCR warmup to DPF regens to Jake brake to counter balancing the EGR gas pressure to plain old making power. If you watch the "Aftertreatment Operating Mode" (or something like that) in Data Monitor when these spool ups occur then you'd see if they correspond with an aftertreatment function.

Could also be spikes in sensor readings that the engine is reacting to. How's you IMAP sensor? NOx sensors? SCR temperature reading? and others? Data monitor is good for watching these values for abnormal or erroneous readings or even just patterns that might give clues.

Rawze might have something more precise to point toward.

if you don't have Insite then you should get and Inline 6 Adaptor and a copy of Insite 7.6 as it's your first go-to for diagnosing engine/aftertreatment related issues.