engines with high compression can have excessive blowby when left at idle speeds for long periods of time, but i am talking diesels, like 18+:1 compression. small amounts of fuel and air can squeek past the rings and enter the sump. over time the fuel breaks down and thins the oil reducing its ability to properly lube the engine. i have also seen rebuilt engines that don't have the rings offset properly allowing blowby. don't really know if that helps or not, but it makes me look like i know what i'm talking about!
i would personally give the dealer a call on this one!
"when i let off the throttle it gets all squirrely, so, i just stay on the throttle.."