1993 Toyota Camry Hesitates, stalls, idles rough, no power

We are having problems with our son's '93 Camry. When he tries to accelerate it hesitates and then is very sensitive to throttle input. If you give it too much input it will just chug and barely runs. It's hard to even get the car up to normal driving speed. Even if you can get the car up to speed, it still has very low power. At idle it runs rough or stalls. Our next door neighbor is a mechanic (40 years) and he can't figure out what is wrong. We've changed the fuel pump, fuel pressure regulator, performed a full tune-up, checked the timing (set correctly), replaced several of the sensors (don't know what they are called), and a number of other things, but we can't get it to run properly after all of this. We have even checked the compression (still good), the spark at all 4 plugs, and the fuel pressure and everything in these areas checks out good. Is there something with this engine that causes this problem that my neighbor is missing? Please help. Thank you!