Please clarify and although it probably does not make a difference in this case please always post the year and model of your car and if you have an optional engine post that as well. Milage also gives us a hint.

Now when you say preassureised. Do you mean that you opend the cap and heard preasure escaping, That's OK.

Just a shot in the dark. Try a bottle or two of Cheveron Techron injector cleaner. Read the directions, you may need two bottles. Let us know how you made out

John Roncallo