Mike, It's called seeking. The engine / fuel system it trying to regulate the air to fuel ratio and it can't. Replace the 02 sensor and if it still does this then it needs a simple fuel adjustment. John Hervey www.specialtauto.com www.deloreanautoparts.com -----Original Message----- From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of mike Sent: Wednesday, July 18, 2007 1:21 PM To: dmcnews@xxxxxxxxxxxxxxx Subject: [DML] Engine Idle Cycles From 1000 To 500 rpms When Engine Warms Up My engine idle is great when I first start up the car. But once the engine has warmed up, the idle will begin to cycle down to 500 rpm and then back up to 1000 or so. Is this a vacuum leak problem or something else? If it is a vacuum problem, can this harmful to the engine, i.e. valves, or just a nuisance? Thanks, Mike #5781 To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/dmcnews/join (Yahoo! ID required) <*> To change settings via email: mailto:dmcnews-digest@xxxxxxxxxxxxxxx mailto:dmcnews-fullfeatured@xxxxxxxxxxxxxxx <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/