Alfa Romeo 156 2.0 ts - Erratic Idle - podz

I have an idel issue with my 156, It drives totally fine but when you come to a stop the revs idle at 1500rpm for 5 to 6 secs before dropping to 900rpm and ticking over nicely. I have chaged the MAF sensor, the air intake pipes and cleaned out the throttle body but still no luck, Has anyone had the same issue and if so how was it resolved