I noticed after my car has been running for a little while I can feel it shake at idle. What would cause this? It doesn't do it when I just start the car for the first time of the day.

It could be a slight misfire or it could be a weak cylinder.
Is it really a shake or more of a vibration and please tell us your idle speed.

If it isn't idle speed it could very well be time for some spark plugs, or even a wire loose on one of the coils. I had a tab bent on one of the plugs, it ran for a whole day on 5 cyl. =) No prob suprisingly....

J

My idle speed is normal. Someone said I could have water in the motor. I ahd the sparkplugs done like 8 months ago. I have never had the coilpacks done. How would I know if it was them?

I have this prob (plugs are good) - had my mech check it out for free and he told me that I'll need new coil packs (he looked at the front ones and told me that they're heating or burning up - the top of the coil pack is turning white on the front 3 lol) and one of the injectors was bad

Get a multimeter (picked up one on sale for $15 at Sears last week) and check the resistance of the coil packs and injectors

Or just wait it out until either a coil pack or injector dies and sets off the CEL

Try a fuel system cleaning...could be something as simple as a dirty intake valve.

When was your last tune-up? Replace your EGR Valve, Fuel Filter, and/or Air Filter.

The latter is some cheaper things you may try.

What eles do I need to do for that?