za_w124_200e is likely correct. A flickering guage needle is highly unlikely to be an actual temperature change. For the most part, a quick, less than a second duration transient of 10 or so degrees would not even show up, much less cause the needle to flicker. The response time of the boss, sensor housing and sensor to temperature changes is much longer than a flickering of the needle you described.
I would start with the sensor by checking its response as the engine warms up. Disconnect it and see what the guage does, then record the signal as the engine warms up by checking resistance, and see if it suddenly goes to zero or infinity. If so the problem is in the sensor. If not, it may be in the wiring or the guage in the dash.
Hope this helps. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)