How often are results faked in computer science papers? Especially in the the more experimental subfields of computer science like systems, how often are results faked? If there is no verification process for any code used, do researchers sometimes fake results to save time?
Nobody knows. Unless someone tries to reproduce the results and cannot, there's not ever even going to be a challenge to the results. Direct reproduction in CS and similar fields is generally done in papers that extend older results or propose a new method. To my knowledge, we do not see a lot of retractions based on these kinds of studies, so I'd say the rate of faking is low. 

Retraction Watch's CS section has about 15 articles in it, but most of them appear to be about retractions for plagiarism not for faking results.