You may well have a sicking EGR valve that is not completely closing after decelleration..
An easy test for intermittant EGR is to pull the actuator vac line off the valve and plug it..then give the egr a couple of light taps to help it seat.
Drive the car and watch for re-occurence...if none, change the egr to the new up-grade [ TSB campaigne] part.
Don't clear the CE egr code til after test...as the test will pop it anyway..
Look for vac leaks at the same time....