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Did you remove the upper intake manifold to replace the spark plugs in the back of the engine?
First make sure you have the coils in the proper order. On the front valve cover near the radiator, make sure the last to coils are in the the proper holes. They can easily be connected up wrong. Also check the last 2 on the back valve cover. The same goes for them.
Swap the last 2 coils on the front valve cover, the ones closest to the transmission. Leave them plugged in when swapping the coils.
The start the engine and see if the engine smooths out.
Also, if you have a code reader, or access to one, check and see if there are any miss fire codes in the ECU (Engine Computer).
Double check the vacuum lines to the upper intake manifold. Also make sure the gaskets are seated properly. They should be replaced if you remove the upper intake though.
Ok. I have seen it done and also done it myself. Just going over every possibility.
Did the vehicle run rough before you replaced the plugs?
Can you drive the vehicle, at least to an auto parts store? They can access any codes in your vehicle for free.
Also, double check the plug wires.
Below is how the coil is numbered.