Sudden Idle burps
 

2005 Mustang GT

Last night I unbolted the air intake box (factory) to grab a wrench that dropped under it, I bolted it back on, and that was that, car was running warmed up and i notice the revs were dropping a little and then smoothing out...the throttle seemed to take just a little more than normal to get the revs up too. and when i let off the gas it would drop low and spring back up to normal every time. why did lifting up the air intake and putting it back down do this all of a sudden? How do I fix?

something is allowing too much air in and the computer is trying to compensate. Sounds like you didn't put it together just right. Back on your heads.

Recheck everything and make sure everything is tight. Start the car without hitting the gas pedal and let it run for about 30 mins without touching the pedal, this should relearn the computer and everything will be alright.