Caravan LE

• 78,000 miles

I believe a tank full of bad gas started the problem. Since it happened, April/05/05, I have had the tank drained, the fuel injection purged, plugs changed (tune-up), and have driven the car until empty twice hoping to get rid of whatever causes the problem, to no avail. Another person who got gas at the same station at the same time has the same problem. The car will sometimes start off without a murmur. At other times it hops, skips, and jumps like a rabbit! When it is completely warmed up it drives ok, but when parked to shop for a period of time, it starts up bad again... or not. It's weird. Some mornings I can get in the car after its been parked all night, and it goes like a dream. So far I have spent approximately $300, but nobody around here seems to be mechanic enough to figure out the problem! No warning lights come on to say it is mechanical. It appears to be something that floats around, blocking one or more of the injectors. It is an old, but very well kept car, with a motor that normally just purrs. The transmission is smooth, etc. It has also been on the diagnosis machine, which showed everything to be in tip top shape.
Has anyone had this problem, and if so, found a solution?
Frustrated.
MoreKool