Check Engine Light and the flake temp guage

My check engine light just came on in my 2000 Jetta GLS 2.0L 8V, the temp guage inside my car is also flaking out, one minute, it reads that the engine is cold after i have been driving for a half hour, then at random times, it will go up to 190, then back down again, like all the way down. i dont have any cash to take it into a dealer right now, nor do i have time, can anyone give me a suggestion as to what it might be and to what, if anything, i can do to fix it.

And now the car is overheating... or so the guage says