My XE has had a stutter at 2.5K RPM right from the word go (about a year!)
Last week I changed the air filter as the 'performance' one was ditched. Suddenly the car was transformed into a stutter free dream. Smooth from idle to the limiter etc. Now, I had changed my filter when I first got the car but it didnt make a difference to the stutter so I though it was something else..
However, after a few hours of driving around the stutter has returned. So, changing the filter does what to the ECU etc? It seems like the car has re-learned the fault that wa 'fixed' by the new filter!!
sounds like coincidence to me,you have probably disturbed something else while under the bonnet doing the filter.
Check your plugs and leads,and check the scre on bit ontop of the spark plugs isnt loose,dizzy cap rotor arm etc.
Remove and carefully check all the inlet trunking from airfilter to throttlebody for splits,a split after the airflow meter can cause havoc as its letting in unmetered air.