The inlet valve on the GE dishwasher has a screen before it on the water supply side. A timer opens the valve for 90 seconds to allow 90 seconds worth of water into the dishwasher. A couple gallons. There is a float switch that shuts the inlet valve before 90 seconds if too much water gets in, but there is no device to prevent too little water from getting in. GE tells you in the guts of the owner's manual that if you have low water pressure, you should purchase an optional high capacity valve (so more water will come in during the 90 seconds.)
Once that water is in the dishwasher, the dishwasher recirculates it for the duration of the cycle. After the cycle, a discharge pump pumps the water out, and if a new cycle is starting, the inlet valve opens up again to let new water in.
During recirculation, the water is strained through a grate, a grinding blade, and then a screen before entering the recirculation pump to keep big chunks of food from clogging the pump. [Edit: these parts can get coated with grease and slime and food particles over time, and cloddfobble's cleaner, as well as manually removing the grate and washing it every couple years is probably a good idea. There are actually a couple grates you can clean in my DW.]
In my dishwasher, if I am correct, the inlet valve screen is blocked with 15 years worth of sand and sediment and not enough fresh water is entering the dishwasher during those 90 seconds at the beginning of the cycle. The pump is starved of water and is blowing air at times. The lack of water and water power results in dirty dishes.
I'll have a chance this weekend to dig into the valve to see if I'm correct. The new part arrived yesterday and below is a picture of the screen on a brand new clean valve. It's actually a big screen because it's very concave by about an inch. More like a screen basket than a screen.
