Originally Posted by ME

My car has somewhere near or over 300,000 miles on it. The engine is not the original engine. The heads, intake, and TB are the only original parts of the engine itself. The block is a '77 305 block because the previous owner ran the engine with pretty much no oil. Anyways, that means if the TB is the original one from the factory, which I have no doubts why it wouldn't be, then the TB is probably due for a freshen up. I doubt that TB was ever serviced. I was watching the spray pattern from the injectors and pretty much it is a mist. However, if you look closely, it appears there are small driplets from the center of the injector dropping into the bore. Now this is where I have come up with a speculation, and you can let me know how close or far off this speculation might be:

If the injector is dripping extra fuel into the engine, the ECU would have to compensate for that by opening up the IAC so the engine isn't running rich, this in turn would raise the idle. The injectors might only leak extra fuel when opened more then what they are at idle. So when I tap the throttle, it opens the injector up and squirts the fuel in to raise the rpm's, but when I let off the throttle, the injector has now been opened and extra fuel can leak out which would cause the IAC to stay open so the engine doesn't run real rich. When the car is up 3 mph the ECU kicks the idle up to help with shifting, well, if the scenario I just described is true, it would exaggerate that kicked up idle since the ECU is opening up the injector.