I have a '95 Olds Aurora which is in great shape, but there seems to be a problem when I push the accelerator down at low RPM's. It backfires from under the hood. I asked the service tech how much it would be to get at tune-up and it turns out it's $665. So i figured before I stick that kind of cash into it, and not knowing the outcome, I'd ask here if that is what it needs or could it be something else. Any info would be greatly appreciated!