Having just gone through a similar experience with my '82 300TDT, I might be able to shed a bit of light on your problems even though I'm the first to admit I'm not diesel expert yet.The valves tend to tighten up over time so if you haven't done a valve adjustment for a while, this could explain the miss at idle. A valve is being held open. I had the same problem. I am told that properly adjusted valves are the most critical component of cold starts. Obviously faulty glow plugs will give you no end of cold start problems. As for the "backfire", if it were a gas engine I would say your timing is way out. Being a diesel, I would imagine the puff of smoke you get is unburned fuel being forced up through an unseated intake valve. The reason the starter seems to surge would be lack of compression on that cylinder. A valve adjustment might cure your problem but if the offending valve has been held open for too long, you may have built up residue on it and it won't seat properly even when it's adjusted. If that happens, don't know if there's much to do but pull the head and regrind the valve. If you pull the head you might as well do the rest of the valves while you're at it. Could also be a case of a timing chain that has finally stretched too much and has thrown the timing out too far. I'd say get the valves adjusted first. While the valve cover is off have the tech check timing chain stretch. If it's out of spec, you won't solve too much until it's replaced. Whatever else you do, never use starting fluid on these engines, if it does fire, you could end up with a hole in your garage roof in the shape of a 4 cyl head. Way too much help for these engines. Maybe others can shed light on something I have missed but hope this helps you out.
'82 300 TDT 330,000 km