OP...your little dip might be a very early...very early indicator of icv with a little dirt on it. Nothing serious...looks like to me anyway.
But, when it starts surging up and down...then search 'idle surge'--there's a massive thread on it...some had mixed results...I posted after I took a trip to throttle body myself and fixed my issue. Don't know when I did that trip...but been idling steady at 700 since...cleaned everything in my path and have written about it a lot...evidently too much...so I'll just let you search!
I'm so depressed. No one wants to come see me in NYC: Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Mangofy your E46!