Focus Acronyms and codes

Could someone post what the heck all these acronyms mean? And only post if you know what they really mean, not what you think they might mean. Also, where these parts are on the car, their function and when they go faulty what the symptoms are.

EGR valve
EGS sensor
DPFE sensor
MAF sensor
..................and so on.

Also, people keep posting about codes. Does anyone have a list of code #'s and what they mean?

Thanks

For the codes, you can usually Google to find their meanings.
EGR=Exhaust gas recirculation valve, and emmissons piece on most modern cars that allows some exhaust gas to be brought into the intake tract and reburned to help the emissions. On the Focus, it's to the right of the valve cover, might be buried under some tubes. It's looks sort of like a rusted UFO, and will be connected to a steel and rubber line. Symptoms are similar to a DPFE going, but it is more likely that it's the DPFE.
DPFE-Depending on who you talk to, either Differential, or Delta Pressure Feedback EGR. It's just a sensor that reads how much exhaust gas is going to the EGR valve, and adjusts how much the valve is open. Most Foci have it mounted on the firewall, but some are right next to the EGR valve, with two rubber hoses and a wiring connector going into it. This is a very common piece to replace on the Focus, especially with a few miles on it. Symptoms include very rough idle, stalling at idle, bogging down under load, or random lack of power from the engine.
MAF-Mass air flow sensor, reads how much air is being brought into the intake tract, as well as the temperature of the air so that the ECU can inject the correct amount of fuel. It will have a wiring connector on it, and will be screwed into the main intake pipe with two screws. Symtoms include rough idle.
I've never heard of the EGS valve, hopefully someone else can help you out, and any more questions, just ask.