Got a '97 2500 diesel. When I start it, the alternator gauge swings from lowest acceptable position on the gauge to normal reading. It generally cycles from lo to high every 4 or 5 seconds. This normally goes on for 30 seconds or so.
When the meter drops to the lowest position, the idle rpms fall way down. When the raises to normal position, the idle goes to normal rpms. What's going on here? Is the alternator getting ready to blow?