The tach on my car started jumping around when my car is on idle, and the volt meter is reading about 11V, but my car idles just fine. What is wrong with my car?

 

Unless you had lights and other major electrical items running at the time, check the smaller wire on the positive battery cable. When it is loose, those are common symptoms.
If you had plenty of other items also drawing power, it may just be that the alt is barely able to keep up at idle speed.

 

Ok, thanks i will check that tomorrow morning.

 

Check the connection on the trailing ignitor too. Might as well check all the connections on that part of the system while you are at it.