GTcarz - Automotive forums for cars & trucks. - 1992 Hyundai Elantra-severe knock/ping under any loading of engine when hot

I have a 1992 Hyundai Elantra with a 1595cc 1.6L DOHC engine
With drivabiltity problems as follows:
First off, the engine starts ok.
When cold, the power often sags off under load for a few seconds, usually
after a shift.
Engine power increases with RPM quite a bit...starting very low.
mild acceleration when cold-you can feel the power step up a 'notch' every
few
hundred rpm increase-like the computer is holding it back...
Throttle response is poor, with quite a delay too.
The engine also sounds very 'sputtery' it hard to explain...

But it is not the engine itself;every so often it will drive better,
sometime very good.
2 days ago I started it and it ran great when cold, no sags at all-and the
throttle
responded well-and the engine did not have the 'sputter' so much.
I tried to get it to ping when warm, and it did not...
(Of course, next day it was back to its tricks...)

When warm, car generally drives better, (but power still weak)
If the engine is loaded for a while,
it then starts knocking and pinging, getting worse as time goes on...
eventually, ANY engine load gives slight pinging, downshifting to get higher
RPM
and lighter throttle does NOT stop the ping....engine power also seems to
drop...
Turning on the A/C makes the car basically undrivable, really saps away the
power...

It acts like the cylinders are overheating, and can't cool off (temp gauge
normal though...)
Possible things:
Low gas pressure (gas lines don't seem to keep pressurized after engine shut
off)-pressure reg?
would force lean running and overheating?
EGR system not working, stuck open?

Any ideas? Have downloaded charts, tested some things myself, checked
computer
inputs (BTW, no codes are set, and check engine light does not come on...)
It's probably 1 little part doing this....
I'd love ANY help here...

Aaron H.