idle question

[heino@ix.netcom.com (Paul Ernst Meyer)]

Pair of questions about peculiar idle behavior on my 1990 200t.   
Sometimes, when coasting down a hill with foot off gas idle fluctuates 
between 1300 and 1800 rpm in 1 second cycles.   This has also happened 
once or twice after putting the car in park after long drives.   In 
addition the car seems to idle high in park.   Any input would be 
greatly appreciated.  Thanks in advance!
                        
Reid Meyer
'90 200t (132k)
'81 5ks (R.I.P)