89 Accord running strangely

I have an 89 Accord DX with about 130k, auto. I bought another ride in October and hadn't driven it more than a few times in the driveway cause the sticker and tags were dead. I loaned it to my brother for a work ride. He drove it ~75 miles to his house, no problem. Goes to drive it to the job a couple hundred miles away, and all the sudden it loses power, won't run over ~30mph and 1600rpm. He stops, shuts it off for 1-2 minutes, starts it up, runs fine. Does this off and on, sometimes often, sometimes not for hours. Recently replaced plugs, wires, PCV valve, ran normal for months after that. Any thoughts?

I had similar problem on a different model car. It would only get up to about 30 MPH and it was very labored at that; like someone had stuffed a potato up the tailpipe. Turned out my catalytic converter had failed. My mechanic said I had gotten a bad tank of gas that may have had some lead in it and that fused the mesh inside the converter when it got hot. Once it cooled down, the mesh would not be fused and so the car could breath. He changed the converter and the problem went away. Good luck.