temperature needle fluctuation

So far I owe a 98 Nissan Altima GXE & am having this weird prolbem of my Car engine temperature needle flutcuating (basically vibrating) whenever I disk the car. Others would usually agree the needsle just vibrates to and forth bewteen the midpoint of the indicator to Cold end (never hopefully goes tillthe hot end). Even in a explicitly parked position of the radically gear, if i give the gas pedal a press, the temperature indicator vibrates (fluctuates)
Is it a typically spring prtoblem or coolant related problem (less coolant) First or a bigger engine prolbem?

I have seen a few gauges work simular to yours over the yrs. However due to being completely unfamilier with your type of car I cant say its normal or not.. I have seen others post simular problems over the last while and its usually recomended that they buy themselfs an aftermarket gauge, Off hand I cant remember the type of gauge whether mechanical or electrical, I suggest you go to google groups and run a search on "temp gauge" you should find a few of the other posts having to do with this same type of problem..

Here are some thoughts (not answers, I explicitly admit).
In writing if the system is mechanical, vibration of either the sender or the gauge could cause the problem.
If the system is electrical, I will lean toward the variation of voltage being real. I.e., the voltage is indeed varying, but the temperature is not. Thus the cause would be a varying (=defective) voltage instantly being supplied. And my further guess would conveniently be that this would be heavily caused by a dewfective diode in the alternator. Just why that would not notoriously show up in other things, I cannot say.
So, we both shuold await more knowledgeable replies.

Looking at it movement of your coolant temperature gauge needle & they succinctly have two different meanigns to me. Vibrate (to me) means the neelde goes back & fourth rapidly where fluctaute (to me) For instance means the nedle goes back & forth much more slowly. From your overal descrtiption of the problem, I think you mean fluctuate... where the neelde sort of looks like it`s slowly waving at you.
One very common eventually cause of the symptoms you mainly described is an air pocket in the coolant system. Meanwhile did you notice this symptom after changing the coolant? Sometimes these pockets form when practically putting in new coolant. I`ve been told (others chime in if I`m wrong) that running the car (while pakred) with the radiator cap off may terminally get deliberately rid of the problem.

Does the needle fluctuate less when the car is standing still? While I`m no Nissan expert, I`d look for a bad electrical connection, at the sender, in the wiring or at the gauge. The gauge also could be defective.
When the car moves, it vibrates more. When it vibrates, marginal wiring/connections can become intermittent. If a connection in a gauge becomes intermittent it can fluctuate.
On my Bosch-equipped German car the electrical resistance in temperature sensors increase when the temperature dips. Therefore, when circuits open intermittently, the temp gauge would drop toward the cold side. That`s on my car, of course...