Hi guys.

I have 2012 e350 bluetec.

I'm wondering about rpm.

The normal rpm is 600 and when dpf work rpm go up 900. So, i can feel when dpf work

Also, in the winter time, cold start and turn heat then rpm go to 900 and when normal temp than rpm go down 600 as normal rpm.

but the problem is weeks ago

when i turn in ac then rpm go to 900 and turn off ac then rpm go down 600. I don't know why

anyone have same thing? or it is normal?

( personal opinion : suspect differential pressure sensor but not sure.)