My Baby is a little sick

[Burgenlander]

Dear Friends, My 96E300D has developed a slight flutter or mis in the 2100 to 2600 rpm range. This has happened after I took it in for a anti freeze flush at an independent but trusted garage. Whether that has anything to do with it or not I don't know but just wanted to say in case that could have done it. I have changed th fuel filter twice now, thinking perhaps water, I see no trace of water. Could this possibly be Injectors?I must say that it is not all the time but I would say at least 75% of the time . I notice no problem accelerating or at higher RPM. AS always any input will be appreciated.
Burgenlander
83 240 D
82 380SL
82 380 SEL