I just got a 1996 F250 7.3, it’s pretty beat up but when I took it for a test drive it ran like a dream. I started it up to go to work and a few seconds after it stalled, I started it up again and noticed the RPMs slowly drop before shutting off. I’m new to Diesel engines but I know to let the glow plugs heat up and all that. I then thought maybe it was a little cold because it was about 50 this morning, so I held the RPMs at about 1500 for a bit while the thermostat gauge came up and when I let off that seemed to do the trick. Can anyone tell me what this might be and if it’s in dire need of fixing.