It could be a few things but I would bet that something with your ignition system needs to be replaced. A poor connection at the battery terminals can cause the cars gauges to do strange things. Make sure they are clean and have a good connection. If any other wiring modifications have been done to the car make sure that those connections are secure as well. (Aftermarket alarm, electric start ect.)
The Tach, if it operates erratic, is probably the tach itself that needs to be replaced or the resistor in the circuit is going out. The nice thing about a 1996 car is that you can hook up a scan tool and get the tach feed to display. The signal is provided from the cluster, where it plugs in, to the computer, so if it reads correctly on the scan tool then you know it is the tach. You could go to Autozone or Checker and get them to hook up their scanner, tell them the problem and you want to see if they can read the engines RPMs with their scan tool. If they can then I would replace the tach. If not, then it is probably the resistor or wiring. But, if the latter was the case the computer would be throwing a code. The blower speed thing is just a matter of changing the blower resistor unit. It is located under the dash on the passenger side and in the blower case. Remove the glovebox and you will have access. Purchase the new part and you will be able to recognize it. All it takes is a phillips screwdriver to do the change.
Monday, January 28th, 2013 AT 9:18 PM