1999 Ford Explorer XLT, 150,000 miles

Lets take these problems one at a time.

[quote:29f2cc2f9c="murphyslaw"]First, when I drive, there is a shaking which starts to get really bad around 70-75 MPH (Could that be a bearing or axle problem? or maybe a transmission problem?).[/quote:29f2cc2f9c]

Could you be more specific with this? Is the car shaking, swaying, vibrating, or is there a growning sound or do you mean you hear something shiking?

[quote:29f2cc2f9c="murphyslaw"]While the car is idling (when it idles) there is a noise under the car like a tin can is rattling towards the front of the car along with what sounds like grinding.[/quote:29f2cc2f9c]

Need a better description of this as well; mainly, there is a lot of stuff toward the front of any car...you need to open up the hood and listen carefully and try to get a better idea of where the sound is comeing from...as you look at the fron of your car, which side of the engine compartment does the sound seem to be comeing from?, is it toward the top of the engine or closer to the ground?, is the ratteling constant or intermittent?

[quote:29f2cc2f9c="murphyslaw"]we simply cannot get the car to idle....we would have to keep our feet on the gas. For some reason it just doesn't catch. The fuel system has been checked and supposedly fixed, but it continues to come back.[/quote:29f2cc2f9c]

First off, how long ago were the air filter, fuel filter, spark plugs, and egr valve replaced?
Is your computor throwing any trouble codes?