1990 e 150 5.0L very hard cold starts, starts ok warm.

van has gotten very hard to start if it sits more than 2 hours. While trying to
crank it, it may take several tries before it starts and runs rough, have to
keep on gas peddle to keep it running, feels like missing / rough, runs like
crap, once a few minuets go by, it begins to "settle down" and run smoothly,
although it has a slight increase in idle. While running, at idle, i can
disconnect air control sensor - and it runs worse till reconnected, unplug
throttle position sensor - no change, unplug the map sensor - it runs worse,
hold hands over the throttle intake, it idles normal, take hands off - idle
picks up slightly. Just replaced spark plugs, dist cap & rotor, gas filter, air
filter, pcv also, new air pump. Otherwise it runs great. it does have high
mileage apx 150k. It blows a little smoke when starts,[cold and before this
issue] and has done this for a while, but no excessive oil usage, gas
mileage is normal.  The mechanic shop i put it in says the plugs are
fowling, really??? they fowl so bad that it does not want to start after a 2
hour rest, when it was fine when I stopped it, and i don't have a smoke trail.  
Hope someone can help.