PC gets limited to 100 Mbps and develops severe lag during use
Asked by
MellowPine47
I'm having several problems that seem to point to a hardware or system issue rather than just my internet connection. My roommate and I have a 500/500 Mbps connection. He regularly gets the full speed, while my desktop reaches only about 90/90 Mbps at best. I've experienced the same problem in different apartments with different routers and internet providers.
I'm also getting severe ping spikes in Valorant and Dead by Daylight. During the worst episodes, the game freezes for a few seconds, audio cuts out—including voice chat—and then everything catches up at once. The problem tends to worsen the longer the computer is running or the longer I play. Shutting the PC down overnight makes it somewhat better the next day, but doesn't fix it.
There are additional system-wide symptoms. My mouse movement has become choppy, Discord camera output can lag behind by three to five seconds, and the single-player game Blue Prince starts normally but then begins running in smooth slow motion after a couple of minutes. The computer's fans have also always been unusually loud compared with other PCs.
My system has an ASUS ROG STRIX B550-I GAMING motherboard, Ryzen 7 2700X processor, 32 GB of RAM, and an RTX 2080 Ti. Reported CPU temperatures are relatively low, generally around 30–50°C.
I've tried multiple Ethernet cables, Wi-Fi, updating the motherboard and drivers, installing Windows updates, scanning for malware, checking for VPNs, resetting the PC, cleaning the dust, and monitoring CPU temperatures. I also tested the same wall network jack used by my roommate without seeing an improvement. What hardware or diagnostic checks should I focus on to identify the cause?
Answers
Because the mouse, Discord audio/video, games, and even an offline game are affected, I’d prioritize troubleshooting the whole computer rather than focusing on the ISP. A faulty motherboard, network adapter, graphics driver, power supply, RAM, or storage device could cause intermittent stalls. Check Windows Event Viewer and Reliability Monitor for hardware, display-driver, disk, WHEA, or application errors. Run a proper memory test, check the drive’s SMART health, and temporarily remove unnecessary startup programs and overlays. If nothing stands out, a genuinely clean Windows installation made from installation media—not the built-in reset—would help separate software problems from hardware faults.
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Try isolating components instead of changing more network settings. If available, use a separate USB Ethernet adapter and see whether the negotiated speed and lag change. Test with one RAM module at a time, disconnect nonessential USB devices, and check the system with another known-good power supply if you can. A defective onboard network controller could explain the speed cap, but it would not normally cause an offline game to enter slow motion, so there may be a second hardware or driver issue—or one underlying power or motherboard problem affecting several devices.
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The broader symptoms sound more like a hardware, power, or thermal problem than an internet-speed problem. The CPU temperatures you listed don’t look dangerous, but they may have been measured while the system was idle. Monitor CPU and GPU temperature, clock speed, utilization, and power limits while playing until the slowdown begins. Also check whether the CPU or GPU clocks drop sharply, whether memory usage keeps climbing, and whether the system drive reaches 100% active time. Loud fans could indicate an aggressive fan curve, a failing fan, or a component running hot under load.
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The roughly 90 Mbps limit is a strong clue that some Ethernet link is negotiating at 100 Mbps instead of 1 Gbps. Check the connection status in Windows and in the adapter’s advanced properties to see whether the negotiated speed is 100 Mbps or 1.0 Gbps. A wall jack, patch panel, switch, or other device between the PC and router could have a bad pair or only support 100 Mbps. However, 90 Mbps is still enough for ordinary gaming traffic, so it probably doesn’t explain the entire system freezing and the single-player game slowing down. Test the PC directly on the same router port and cable path as the other computer if possible, and inspect the link speed while the issue is occurring.
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MellowPine47: I tested the same jack and several cables, and the behavior stayed the same. The issue also existed before I moved and changed providers, so I’m increasingly suspicious of the PC itself.