How do I fix lag spikes? in L4D?

I use a modem and its directly connected to my computer. I disable multicore rendering. I turned antivirus off. I'm pretty sure I tried everything. Tried resetting modem and router. It started maybe three or four days ago. I haven't changed anything on my computer. I think it might be the servers in l4d1 and 2 but I highly doubt that. Whenever a horde or more than three zombies are on my screen my ping will sky rocket. Or whenever I'm a hunter and try to pounce I'll start lagging really bad. And it'll show my ping start to rise. I looked up a lot of things, but I'm just tired of looking and searching.