okay i have a 2001 honda accord v6 and basicly the tach bounces from 500prm-300rpm then back up agian and it repeats it does it when the headlights are on or when the ac is on when idling and the dash lights would dim and when driving the needle will be bouncing at any rpm. could the battery be bad? any ideas would help thanks!

 

If engine speed is normal (700-800 rpm) when tach is bouncing, I would suspect a bad alternator (low voltage output). Have an alternator and battery check performed.

If idle speed is actually very low (300-500 rpm), the problem might occur under heavy electrical load; inadequate voltage w/ a good alternator. In this case you need to clean the idle air control valve, throttle plate, and throttle body bore to restore idle performance.

good luck

 

If the engine RPM is actually bouncing, then you can go over all the normal things for surging idle.

 

okay i the alternator tested at autozone and they said its bad so i got another one from the junkyard and its still doing the same thing. should i just get a brand new one?

 

Maybe the junkyard one is bad too? I'd get a new one, but it's pretty easy for me to spend YOUR money.