Check engine goes off every 3 to 4 months?

Hello, from a quick look at the engine exploded view, the spark plugs are installed through the valve cover, correct? There are round seals that seal out oil from the spark plug tube, if you're getting oil onto the spark plug then those seals are leaking, Ill post a diagram. When oil gets onto the spark plug, it causes a cylinder misfire because the spark plug fires outside the cylinder, being that's its cover in oil, it easily causes the spark to jump to the spark plug tube instead of firing inside the cylinder. Hence the cylinder misfires, this condition will eventually damage the catalytic converter due to raw fuel going down the exhaust. I will post further service info and look into the valve cover gasket set for you.

The 1st diagram is just a view of the engine components, diagrams 2-6 are for replacing the Valve Cover gasket and spark plug tube seals. Unfortunately the upper intake manifold has to be removed to replace the valve cover gaskets, I know on these engines the intake manifold covers quite a bit of the engine, so a new gasket set will be needed for the intake manifold as well, I will post the service information and torque specs on this as well.
I had a vehicle with this same exact issue a few days ago, the cylinder misfires would come and go as the vehicle was driven, as would the check engine light.
You will need to also check the ignition coil boots, since they also are installed in the spark plug tube, the ignition coil boots can become saturated in oil and once that happens, they are no good anymore. The spark can jump even easier since there is poor insulation between the coil and spark plug.

Here are the steps and instructions for removing and installing the upper and lower intake manifolds. They have you remove the throttle body, but I think you can get away with leaving it on the upper intake manifold, that you'll have to check out when removing it. There is a single gasket for the upper intake (Plenum) and the lower intake manifold (which is labelled as "Front and Read Injector Base" which requires 2 gaskets, this also is something that may or may not need to removed, If you can remove the valve covers without having to take the lower intake manifold off, I would take that route. There is also a coolant refill procedure I can post if you're going to do this work yourself.

Glad to help, this is the coolant refill info, they have you raise the rpm and recheck the coolant level, but dont open the radiator after the cooling system is up to temperature. I usually just fill the cooling system and start the engine with the radiator or reservoir cap off to allow the air to escape, once the thermostat opens the coolant level will drop and can be topped off or use a vacuum fill coolant system which works really well. Its what I use now when filling any coolant system, you can get one at Harbor freight for pretty cheap, it uses shop air to vacuum the complete cooling system, then draws up the new coolant threw a separate hose and fills the system really quick. Last diagram. Its worth the investment if you work on cars enough.