I have since today a very ribbling (don’t know the english word) effect on the sides of my print. They have the pattern of the ribbons, so i loosend and retention as the wiki says here: Bambu Lab P1 series printer Maintenance Recommendation | Bambu Lab Wiki on the "Idler pulley"section. But it did not improve the quality.
You can see in the pictures the same part printed a few months before and below the part today.
What do i need to do to fix this?
Have you cleaned the carbon rails and lubricated the steel rails?
Yes, twice. Loosend and retithend the iddler pullies after that.
I think the term you were looking for was “rippling affect” 
in case you want to Google-search it elsewhere. Either way, the images are very clear so thank you for posting that.
You may be making an assumption that simply because you achieved a desirable result a few months ago, that the hardware is at fault. I did not see you mention it but, before I dive into invasive hardware related tinkering, I always try to see if I can manage the print via slicer settings. Diving into hardware remedies before exhausting settings experimentation is more than likely to make matters worse. Did you attempt any changes in the slicer?
Here are some key questions:
Is this the same spool of filament? Is it PLA or some other filament?
Did you attempt to recreate the rippling affect using a simplified model like a cube primitive? You could also try printing a simple calibration cube and posting the results here as this will allow the community to see a known reference model to compare to.
Have tried slowing the print down using the “Silent” mode on the printer panel to see if you can get a different result? This troubleshooting technique is best when paired with a test model of known origin like a calibration cube as it allows you to witness first hand what you’re look for.
Did you try manually recalibrating your filament?
Same spool, it is PETG.
This looks to be my problem: Banding / Ringing type artifacts? - #507 by kip
I guess i have to speed up the printing
PETG? I was hoping that would not be the case. Did you dry the filament spool recently? How are you storing it? I ask because PETG is very hydroscopic. Forget what I said above until you make sure your filament has no moisture. The only way to determine this is to weigh the spool before and after you dry it, otherwise you simply won’t know if moisture was the cause.
You don’t need a fancy filament dryer to test this out. You can use the bed of your P1 and use the cardboard box the spool came in as a cover.
This video will cover the topic.
Here’s a Bamb wiki on the topic.
Before I got my dryer, it’s what I used to dry my filament. However, it will tie up your printer while it’s drying.
But one warning. For PETG, you might be tempted to heat the bed to 75C… Don’t do that. Why you ask? Here’s why. 
Here’s the DIY example of what I used when I first started drying filament using the heat bed. It was effective.
