Oldsmobile/Buick Repair: 1990 Lesabre running rough, buick lesabre limited, vacuum leak

Question
Hi, here's a problem I have been having with my 1990 Buick LeSabre Limited, 112,000 miles on it. Recent tune up(plugs, not wires, O2 sensor, air cleaner, passd emissions). After driving for about 30 minutes, the engine idles faster, and runs kind of rough. Sometimes it will go away by itself, sometimes it will stay until I park, let sit 5 minutes and restart. I notice if it's running rough, and I try to travel at slow speeds like when parking and the steering wheel is turned quite a bit to one side, the car will die out. Any ideas?

Answer
Hi Brian,
Sounds like a vacuum leak, but I don't know why it waits till it is warm.
The EGR valve seating on some carbon could cause that, and it doesn't open and close till it warms up.
Doesn't explain why sitting would help it.
A vacuum forming in the fuel tank can cause stuff to act wierd.

Van