1991 Other Hyundai Models Rough Idle, Low Power. Is it th

About 6 months ago, my '91 Hyundai Excel started acting a little wierd. When I first start the car, it idles very rough, and when I'm on the road it feels like it has very little power (even going up small inclines). However, when the car warms up a bit, after driving for 10 or 15 minutes, the idle is much more smooth. My Dad and I have replaced what WE thought was wrong with it, but its still doing the same thing. We first replaced the spark plugs, and the spark plug wires. We then replaced the timing belt, TB tensioner, fan belt, water pump, o2 sensor, air filter, fuel filter, pcv valve, and thermostat. We were hoping that it was the timing belt (as it needed to be replaced anyway), however, none of our fixes seemed to make even the slightest difference. I took the car into a mechanic and I was charged $100 just for a compression test. They said that there was a problem with the compression and they thought maybe the timing belt was the source of the problem. I assured them that we had just changed it, and that before we put the belt on we checked multiple times to make sure that the timing was right on. They wanted to charge me hundreds of dollars to check what I already knew wasn't the problem, and since my car is probably only worth a couple hundred bucks, I wasn't willing to pay that. So I took the car back home and my Dad and I double-checked the timing on the belt. We used a screwdriver to feel if the piston was moving up as the timing belt reached the right mark (just to make sure the actual "mark" wasn't off somehow) and it was right on. The only other thing we can think of is the EGR valve (which wouldn't explain the poor compression, but it might explain the poor idle and low power, right?). So last night we unhooked the hose from the EGR valve while the car was still running, and it didn't effect the way the car was running even one bit. That makes me more confident that it IS the EGR valve, because if you can take a part off a car and it still runs the same (poorly), thats probably a good sign that the part isn't working, right? The problem is, when we took the EGR valve off to check it, it seemed to be working fine. There was some carbon build up in the valve, but as we blew into the hose on the valve it seemed to move up and down just fine (reacting to the "vacuum" effect). What would you recommend I do? Should I clean the EGR valve? If so, how do I clean it? Should I buy a new one (even though the old one seems to be working )? If you don't think its the EGR valve, what else could it be? Is my car just too old? It has to pass emitions within the next few days, but it won't if I don't figure out the problem, and I'll have to either sell the car for a couple hundred dollars, or donate it to the kidney foundation or something. I would rather keep it, obviously, because it would mean no car payments for possibly another year (hopefully). Please help!