Code P2004

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This is a very common problem on these cars and it's not a critical issue. There are flaps in the intake runners that open and close to increase low end torque. Most often the vacuum lines crack or the flaps get stuck. Occasionally the control valve will go bad.

Since you notice an idle issue it could be a vacuum leak. Check all the hoses running from the intake to the Intake manifold runner control solenoid and IMRC module/actuator and intake. I believe the hose is 3/32" if you need to replace it.

Next if that's good disconnect the IMRC actuator and see if you can move the rod by hand. If it doesn't' move you'll need the flap kit. I cannot find a link right now but I believe the last set I bought was around 80.00

So next if the hoses are good and IMRC flaps move you need to get a hand held vacuum pump and connect it to the IMRC actuator and see if when applying vacuum the flap arm moves. If it does then the actuator is ok, if it does not the module has a hole in the diaphragm and is bad.

If all above is good then the control solenoid is likely bad.

Below is a diagram of the system. I highlighted the parts to look at and vacuum lines. It's not too hard to work on once you find all the vacuum line. The one on the solenoid is hard to see unless you are under the car.