temp sensor problems?/questions

[theonlykid]

i am new to the whole car repair thing and am trying to learn it, and i have a couple of questions about my temp sensor( 190E 1992/2.6). i think i need a new one, but perhaps someone could confirm that for me. also i am confused about the color of the sensor. everything i have seen on this site or others says that that car should either have a green sensor at the back of the head drivers side( thats where mine is) w/ 2 plugs for the harness to plug into, or a black one w/ 4 prongs on the intake manifold( i think). mine is on the head and is blue!! what gives. definatly blue not faded green ect... the reasons why i think i need a new sensor: the car has gotten incresingly hard to start, sometimes i need to step on the gas and crank at the same time, when it turns over the rps are way high 1500 +/- 200. they come down when it warms up. i have had a rapid drop in gas milage from aprox 18 mpg to 11 mpg. the o2 sensor was replaced as well as the plugs. the car is not getting up to temp at all, not just because its cold out either(20 degF at night). the temp gague needle has not hit 80degC in at least a week. thats where it is usually in winter time, and it takes at least 15 min of idle time to get off of 40 degC. the other thing that i noticed is that the speedodometer needle has started to jump arround. when its cold its the worst and when it warms up its almost unnoticable. i know its a 50 $ part, and my car drives like ****. any help is welcomed. i want my BENZ back.