Hi Guys, I run into this wierd issue.
Bought a used Mac Pro 3.1 a while back. it's a 2 X 2.8 model with a HD2600XT and 1GB RAM. First thing I did was more RAM. I got 12 GB in pairs in there now. I did a fresh install of 10.10. I notice the computer will lag a bit every once in a while as if if got hang up on a disk access or something. I was hoping 10.11 would help...Guess I was wrong. I also upgraded the video to 5870 hoping that would help. It didn't help much.
I was kind of living with it. It's only doing that every once or twice in a hour. Then it started to get worst in the last 6 months to once every 5-10 min. Started running activity monitor. The CPU load is always from less then 1% to about 27%. Memory used is only about 3GB out of 12GB. Not much Disk activities or Network activities. The system should be running very smoothly with these loads.
In the last 3 weeks or so, it got worst again. Every characters I type it freeze with a beachball for a few seconds. Reboot helped. But it would start doing that again in a few hours.
My Mac pro 1.1 with 2 X 2.66(4 cores) running 10.11 is smoother then the 3.1 with 8 cores. I got another Mac Pro 3.1 with 10.11 as well(I still like 10.10 better). It's running fine.
I swapped the RAMS between the two Mac Pro 3.1 already. So it's not the RAM or the riser card.
The computer is sitting in an unheated garage right now at -4C so I don't think it's temperature. I have also blown all the heatsinks and fans clean with a spray can.
Any idea or guesses on what's wrong? I am thinking of pulling the heatsink apart next and put fresh thermo-paste on them.
Thanks for any suggestion in advance.