Erratic Temperature Gauge and Tachometer

[udengineer2001]

I have two items that may be related and may not be.

Item 1) The temperature gauge flucuates. It never goes above the 1/2 mark. It will drop to the bottom of the dial and then fluctuate between 0 and the 1/2 mark. This will occur with or without item 2 occuring.

Item 2) The tachometer will jump around. It does feel like the transmission is shifting down and then back up again. When this occurs the temperature gauge is also fluctuating. In fact 80-90% of the time it seems as the though the temperature gauge movement corresponds to the movement of the tach. When this occurs it will occur several times in a row and then will not occur for a while.

There are no noises. The car accelerates great and maintains velocity fine. It is just very concerning to be driving down the road and have gauges fluctuating and the engine or transmission driving up the engine speed. I am thinking it is a sensor or electrical problem of some kind.

Any suggestions would be great.
Thanks,
Jeff

[udengineer2001]

Well I finally took it to the dealer. The diagnosis was a loose terminal on the temperature sensor. This caused the following:

The temperature would sense between -35F and ambient temperature. When it sensed -35 which was significantly less than the ambient it:

Modified the fuel mixture-which made it run like crap.
Downshifted-The car is designed to not be in overdrive in extreme temps.
Increase the temperature and blower speed in the passenger compartment-Climate control
Who know what else.

This explains why it acted up more in the afternoon then morning-bigger temp difference between morning and evening.

Hope someone finds this useful.