over the last couple months my ford focus has been stalling, and it basicly started happening right after i put in my cold air intake, so i took it out and put the stock one back in and the stalling continued. so that eliminated the cold air intake. Then i was talking to my uncle who works or fords and he told me that the pcv valve hose thats behind the engine connecting to the intake manifold, that on fords the vaccumm is so strong that eventually the hose collapse which is causing my rpm's to go up and down and depending on how hard the hose is sqeezing that will determine if my engine will shut off. so i check it out and i found the same collapse on my hose. I'm hopeing this is the problem i won't know for sure until tonight (friday) when i put in the new hoseing and the new pcv valve ( the only reason why im doing the valve is because if im going to be working on that hose im going to change it while im down there) but ill keep you guys posted and let you know if that is the problem.