Ok i've diagnose that the alernator is failing. Brake and Battery lights coming on. My question is, would a bad alternator also cause the rpm needle jump up and down? It revs up and down also but the rpm needle is very erratic. With the ac on it doesn't do it, but when the compressor kicks off it starts again until the compressor kicks back on. I;ve changed spark plugs, wires,distru,coil. Can a bad altnerator cause an erratic rpm?

 

Yes, because it is not getting the required constant power to operate correctly.

 

i'll go ahead and buy a new alternator and change out the old one.Hopefully this should fix the problem

 

Good Luck !