1987 Mazda RX7

Check out the catalitic converter, with it cold tap on it and see if there is any internal rattling or noise. What happens is that the converer breaks apart internally after time. This will restrick the exhaust flow and make back pressure so the engine looses power. You can also see if the catalitic converter is clogged after you have driven at night look at the converter when dark, if it has a glow of red it is probably clogged. Most times they don't clog all the way. The engine may run fine until higher rpm's then it limits the amount of exhaust. To find a mechanic depending where you live is in the yellow pages. Check foreign car repair.