So, a not very nice friend of mine modded the [censored] speedmult into 1000, and of course, now my character is so fast I can't actually play at all cause when I move I find myself 1000 miles up in the air and game crashes. As I try to enter player.modav speedmult into 1, 0, -1 or even -1000, this has no effect and my character is still too fast, and my best save is totally unplayable. I really don't want to lose this game so please, can anyone help me?

//And please don't tell me to load earlier save, I would if I had.

Well how did he change it? If he went into the CS and made an esp for the change, you'd simply have to delete that esp. If he did it through the console and your attempts to reset it have failed, you might be out of luck. You might be able to use a save game editor, but I personally don't know of any. Maybe try a search on the Nexus.

I completed to get back a earlier deleted save, this problem is kinda fixed. Thanks everyone.