Avaris

Afternoon I had Napa replace my alternator on my 1998 Cheverolet Monte Carlo Z34 v6 a while ago and ever since its been idling strangely and giving off a very strong exhaust smell. My first though would be that they might have thrown off the fuel to air ratio when they worked on it because getting to the alternator requires a ridiculous amount of removing vital component. If anyone has an idea on what the cause might be any help given would be much appreciated I'd rather it not lead to something worse it already cost me $600 just to replaces that alternator.