Well, I had a misfire issue w the same code very recently and the cause was the plugs. Apparently, I didn't tighten them enough so the vibration caused the grounding to points break off. Maybe the mechanic did the same thing I did. I solved my problem w new plugs and making sure they were on right. I had no idea what misfire was until this experience. It almost feels like the car will stall then surge, almost like a messed up tranny.
By the way, I doubt it is the intake. If u had a vacuum leak from improper install, your idle would go up and down erratically. Try it... I did it on accident during the install. Misfire and vacuum leak feel completely diff on the fx or any car.