unusual idle while only in park

97 Regal LS 190kms

Hi when the car is on and in "park", the idle is inconsistent. Rpm tach needle moves enough to notice. Drives fine in "drive" I've lifted the hood and it sounds like the "chugging" is coming from around the alternator area. There is no service engine light on. Im wondering if this is a sensor?


side notes: -had fuel filter replaced last week..
-used engine replaced Oct/2010.

Any ideas/feedback appreciated


Thanks!

Update on rough idle: had a friend mechanic take off engine cover, noticed a vacuum line was loose. So he secured it back in place and now the car is at normal idle. Will continue to start it up and let it run to monitor any unusual sounds.

Im wondering what vacuum line this is? Any ideas?
thanks!

A vacuum line is used for some type of switch, any leak would of caused your idle problem.

do you know what area the vacuum line was in? There are many for underhood components like the canister purge valve (mounted to front of UIM), fuel pressure regulator, HVAC vacuum supply, etc... just to name a few.

I will ask the handy man who re-attached the line and update the forum. I remember when he pulled it off completely there was a "hissing" like sound..

Thanks for your insight, you sound very knowledgeable about these Buick's!