eratic idle on new engine rebuild

Hello all I have an 88' mazda b2200 which I just rebuilt. Since I have no previous automotive experience I'm hoping someone here can offer suggestions on how to fix the problem I'm having. The engine (2.2 litre 4 cylinder, carburated) has new pistons ,rings and bearings, new water and oil pumps, new O2 sensor, new clutch, pressure plate and throwout bearing. The engine idle is eratic, constantly going up and down both when the engine is cold and warmed up. If I set the idle speed to the recommended spec (800 rpm) it sounds like the engine is going to stall. It starts to sputter, so I have to set the idle rpm higher than normal. I have a timing light and the timing is right where it's supposed to be (6 degrees b.t.d.c,) I've just had the truck emissions tested and it passed no problem. I suspected a vacuum line so I replace all of them-every single one. No change. I put on all new gas lines-front to back plus a new gas tank and sender unit because the tank and the lines were rotten. I rebuilt a carb from the wreckers and put that on thinking maybe the old one had a leak. No change. I replaced this little thermal valve on the underside of the intake manifold (new from mazda $60). Still no change. I put on new spark plugs and wires. No change. It's also got a new rad and cap and all new coolant and power steering hoses. I feel like I'm running out of parts to replace and would really like to figure out what this problem is being caused by. Any suggestions are greatly appreciated, Thankyou, R Thompson