Girlfriend's 94 Concorde shaking violently at idle

[Nightrage]

My girlfriend's 94 Concorde shakes very violently at idle, but it's barely noticable once you start moving. She said it just started happening today. We checked the car's fluids and everything is fine. All of her gauges are reading normal and it's not throwing out any codes. Does anyone have any ideas as to what it could be? Could it be a broken motor mount? The engine is shaking pretty hard, but there's also something clicking under the car. She doesn't pump her own gas, so is it possible that the attendant put 93 octane in rather than 87? It shakes extremely hard. Could the wrong octane have that much of an effect?

Thanks in advance

[Crazy Canuk]

It could be a missfire.

Look at the wires/plugs and see if there ok, I have been told if you look at your engine at night you may be able to see a flash of light if it is the wires, I had my wires go though and I couldnt see anything at night.

This probably is the first thing to check.

actuly I reread it and you mentioned it went away while moving, a missfire should happen all the time but I would still look there first.

[Jeff_in_Atl]

I'd take the air bypass valve and clean it. It controls the amount of air going into the engine at idle. They are notorious for getting carbon in them and sticking closed. That causes a major over rich condition making it idle rough.