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It's is somewhat starting to sound like the FI system is catching the blame for some other problem. I'll just start tossing out some possible things:
1) It's not likely, but an injector could be flowing weakly, but not completely stopped up. You can shade tree check injectors by releasing all 4 sheet metal collars on the injectors, giving each injector a little twist to release the stiction, and then carefully pulling up the whole fuel rail, with all wires and hoses still attached. Then turn the key on several times, without cranking the motor. leave the key on, go up by the motor, then watch the injectors as you slowly pull the throttle open. They should fire in pairs. Any one flowing weakly enough to cause a noticable driving issue should be visibly weaker than the others. Sometimes they refuse to fire at all, but that makes for a very uneven idle.
2) Most likely by my guestimation (discount heavily by lack of information!) is the ignition system. A weak ignition system will often fire just fine at idle and part throttle. But as the compression pressures rise as the throttle opens, so does the resistance of the spark gap, and eventually the spark will refuse to jump. Make sure the points are gapped properly so the coil gets the right amount of on and off as the motor runs. Make sure the plugs are gapped properly (more important on a stock ignition system). A bad condensor will also weaken the spark. You should have a nice fat blue spark, a thin, thready reddish spark won't consistently fire the cylinder.
3) A sneaky thing can be a worn cam lobe. As the lobe wears, the valve opens less and less. This has little impact at idle and part throttle, because the cylinder can still get enough air through the reduced opening. But at higher throttle settings the reduced opening becomes a restriction, and that cylinder will start to fall behind the others. This isn't an all out miss at first, just a slowly growing unevenness that comes on rather slowly. Eventually, the lobe will go completely flat and it will miss at idle too. If it is an exhaust valve it can cause some backfiring and popping as the burning exhaust gets whoosed back up the intake. To diagnose, pull the valve cover and eyeball the valves as you crank the motor over several times. No need to carefully measure, because by the time a lobe is worn enough to make a perceivable difference in running, the reduced lift will be very obvious the the eye.
4) Leaking compression. A variety of reasons, cracked rings, burned or tight valves, cracked or holed pistons. A quick shade tree check to spot a cylinder with weak compression (but not to check for overall wear) is to pull the coil wire, then crank the motor over several times as you listen to how much the starter labors over each compression. Any cylinder with compression down enough to affect running will give the starter a noticably easier time. Whir-whir-whir-whee - a problem. Check for tight valves before anything else (although, it must be said, tight valves usually only occur when valve seats are recessing!)
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I'm JohnMc, and I approved this message.
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