Hi Thank's for the answers!
I use a Prusa i3 Hephestos. I tried the following things:

Speed slow. (20) - the same.
I changed the x - axis Extruder holder, there was a bit play to the ballbearings.
Nothing.

I printed a small testcube - it seems to be really good. the larger the object is, the more the failure comes in.
0.3 resolution is better than 0.2
Here's the cube:

20160216_171224_001.jpg

Only one of the last layers is getting worse. The first layers are most of the prints good.

I have not a working fan at the moment, it is hooked at D9 but not working.