Odd jerk on startup

[JBG]

posted about this a bit ago, then the problem disappeared, and now is back. I have a 85 TDT wagon, running grease. However, this issue is upon startup on diesel...basically, the after starting the car, maybe 10 seconds in, the car starts to act fuel starved or like air is getting in--it jerks and idles hard. Each time it jerks, some white smoke shoots out the tailpipe. After giving it some fuel it evens out, but after putting it in drive and running at low speed (5 mph to a stop, and upon starting from a stop) it runs rough, like at low rpms it's not getting enough fuel or air is getting in. Once the car is fully warm, it's fairly unnoticable, maybe just a slightly hard idle at stoplights.

Is there anywhere obvious to check? And what should I be looking for? I was idly speculating that maybe the air filter is clogged...will check this soon. Any other thoughts?

Thanks, wise ones.

JBG