I honestly have to say that I cannot tell you what is wrong witht he car yet with the info provided..

BUT: If you have had the car for years OR just bought the car and don't know the condition of the engine mounts, replace them they are rather inexpensice compared to the engine shocks.. ($100 engine shock pair v.s $25 engine mount pair)

if this fixes the problem, great.

before you do this, check your idle speed RPM (you can use a engine analyzer from Sears $50, but you will use it often on tune-ups if you are a DIY person) with it you can check your voltage.amperage, RPM.

you will need a 8mm & 6mm Allen to replace the mounts (not the allen L shaped one. You need the Allen that comes in a socket so you can use a "ratchet wrench."

Also check your timing...
after these are in spec:

you may also have a vacuum leak, take some wd40 (some may disagree) and spray along the vacuum lines, if you get a surge, etc.. replace/tighten vacuum hose(s)

then go further into checking your fuel system (start by checking the fuel pump relay and end with the fuel pump.. (cheapest part to most expensive)

Last thing you want is to buy something you didn't need right?
I am in the middle of figuring out a similar problem, so If I find something, I will let you know ASAP.

forgot: ENGINE MOUNT SHOULD BE COMPLETELY TIGHTENED ON THE ENGINE.. NOT LOOSE.
Do the same! :-)
Good Luck.
-Rafael