Hard starting Audi

This '91 - 200 Turbo non-Quattro always starts, but not without some reluctance. 

Symptoms are as follows:

1) Under normal conditions (any weather temp > 5 degrees C) after resting for more than 20 minutes, the engine usually requires 20 to 40 seconds of starter cranking before productive or sustained ignition firing begins.

2) Once firing commences and the starter is disengaged, firing is rough and uneven.  Quite often, a little modulating or outright revving, for 10 to 30 seconds, of the accelerator hastenes the arrival of smooth, steady-state idle.

3) When air and engine temps fall below -17C or 0F, the car will start, like all the other CFI - Audis/VWs I've owned, within the first 2 or three crankshaft revolutions.  Curious enough, a smooth idle occurs right away (akin to my former and current Audis).

4) Like deep cold-weather starts, if the vehicle has remained at rest for more than 3 or 4 days, regardless of air temperature, it fires (within just a few seconds of engine crank) and idles almost instanteously.  This was observed after returning to the vehicle left in long-term parking at the airport following out-of-town business or vacation.

5) Some, not all, rough starts exhibit a little more than normal white/blue exhaust smoke.  The engine consumes about one quart of oil for every oil change (see below).

Maintenance is regular, it receives new motor oil and filter every 3 to 4k miles and the air filter is changed each year before VA-state inspection, which it routinely passes. 

Previous check-ups confirm that fuel pressure remains even at the injectors prior to starting.  Can't confirm cold start valve since deep-cold or long rested starts are normal.

Any ideas or observations and remedies of similar aberrant behavior would be greatly appreciated.

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