Repost: 88 80q Not Running while Warm

[Quattro8880 at aol.com]

Well not exactly. When it gets warm enough I beleive it's vapor locking. The car dies and I remove the gas cap, replace it and the car starts right up. But now the idle bounces up and down over about a 200 rpm range.
 
Cool it off - restart - everything is fine until it gets hot enough again.
 
It's not over heating but this only happens when the car has run for 1/2 hour or so. In other words it's hot not warm.
 
Strange behavior - What could it be ?
 
TIA