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Hello Catdaddy and welcome to Just answer.com, Super mechanic here. About your Galant.
Could it be that you are feeling the engine vibration more than you should?
Like a motor mount? Can you feel it in reverse?
Will it go away if you give it a little gas while holding the brake in drive?
That will help to narrow it down. You want to make sure there are no vacuum hoses that may be cracked or leaking. You might want to switch the coils and see if the code changes to a different cylinder.
Look at the spark plug boots to see if there is any small cracks in them. If it is not ignition related then there might be a problem with the #3 injector, maybe clogging up or a bad connection at the wire.
If it got better with the injectors being cleaned that might be an indication that they are dirty, on the inside.
The best way to clean them is to runa cleaner through them. There is a micro-screen inside them.
As far as the idle problem, not compensating. You might want to do a good throttle bldy cleaning on it. The idle air control valve may be gummed up and getting slow. See if that will help it to run better too.