Okay, to start, my car has 126,000 miles on it. There has been no real work on the motor, just normal sutff (plugs, wires, coils...) Here's the problem.....

All of the sudden, my speedo and tach will fluctuate abnormally if I have the A/C on, or the manual fan switch on, or a combo of that. It is as though there is a power problem and the computer is getting too many volts/amps. If I am sitting at a red light, and have the A/C going, then sitting still my speedo reads around20-30 mph and the tach goes up to around 3000 rpms. I can rev the engine and make both needles climb, but they are not sinchronized (i.e. the speedo does not rise in accordance to what the tach says, visa versa)

Can anyone please give me a solution??? There is no SES light, otherwise I would use my scanner on it. Let me know please!!!

 

I had a problem very similar to that. It was caused by my alternator going out. The needles would jump around then after a little while they would correct themselves, so I just ignored it. After a couple of months the alternator died on me on the interstate. After I had it replaced the problem corrected.

 

my car had a similar problem. make sure your battery connections are good and tight and free of corrosion.

 

The combination of manual fan being on, A/C, and an older alternator/battery/charging system will likely lead to fluctuations which will mess with the electrical system.

As posted above, clean the connections, etc, and maybe get your alternator tested.