Originally Posted by
DmaxMaverick
Welcome aboard!
If you're getting limp mode and/or defueling, check for DTC's (trouble codes). The SES lamp should be on, at least while it's happening. The codes should remain in history for at least a few warm-up cycles, so check for them at your soonest convenience. While it could be a vacuum pump issue, your HVAC controls are all electric. Your vacuum pump should be producing about 20" hg at idle, at the pump outlet (more is better, but 20" means it's enough to not cause issues). Original vacuum plumbing on a 20 year old rig is always suspect, as well.
Hard starts can be caused by a dozen things (some times all at once). If your Wait to Start lamp is coming on when it should, check the harness and individual glow plugs. If they show continuity and/or near a dead short (a few ohms at most), they are likely good.
Could be a head gasket or other cooling system issue. If you have no external leaks, or no other obvious indications of a coolant leak, change the pressure cap (change it anyway, they're cheap). If it continues and pursuing head gaskets isn't an option, go the a GM dealer parts counter and ask for "Cadillac Tablets" and add them to the coolant. They are coolant sealing tabs that work better than any others for minor leaks, often including head gaskets.