Computer help forum: Is it safe to stop System Idle Process??.

Given the age of the system and the symptoms you describe, I'd suggest you start by googling the XP DMA bug.

You'll also have to understand the limitations of the hardware you have. So if some site redesigns things, or just quietly adds in a bunch of tracking scripts for advertising networks, that will impact your system much more than someone with a dual-core CPU for example. Since you're using Internet Explorer, there's also the very distinct possibility of malware having made its way onto your system. Sorry to say, but even visiting "safe" sites isn't always very safe in IE, if ne'er do wells compromise the servers that provide ads to various sites, or are clever enough to quietly break into (for example) CNet's systems and then just insert some seemingly innocuous bit of code to the site. You make just a one or two line change to a web page that might be hundreds of lines long, and it could be week or even months before anyone notices. If CNet gets say 10,000 unique visitors a day, and each one of them is being fed that compromised page... You do the math. IE simply is not safe to use for any amount of time. You should replace it with either Firefox, Opera, Chrome, or Safari. You can take your pick because the important thing is you're not using IE, not which browser you choose to replace it with.

As for your question though, the system idle process isn't really a process so much as just something that has to be there. It's like the "number" zero. If you ask any mathematician, they'll tell you it is required for any kind of complex math, even though technically it's just a placeholder, and has no value. That's more or less what the system idle process is. Even assuming you were able to stop it, then you'd just crash the entire system because you would have taken out the operating system's ability to control the idle state of the CPU. So as soon as the CPU hit an idle state, and that happens a couple dozen times a second, even when the CPU is at 100% utilization, there would be no way to bring control back to any other function of the OS and the system would crash. So however bad the symptoms might seem, that particular cure would be even worse than the disease.

The SIP is not consuming cycles and your first encounter with it may have you come away beat up and sore and maybe feeling a little sheepish.

There are lots of web pages about this process so rather than duplicate it, I'll just tell you are chasing the wrong thing.
Bob