2000 N* Rough Idle in Seville STS
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Results 1 to 6 of 6
Northstar Engines and System Technical Discussion Discussion, 2000 N* Rough Idle in Seville STS in Cadillac Engine Technical Discussion; At 50,000 miles, my 2000 STS began to develop a very mild case of rough idle. Every few seconds the ...
  1. #1
    SmoothTS is offline Cadillac Owners Member
    Automobile(s): Cadillac
    Join Date
    Jan 2008
    Posts
    72

    Question 2000 N* Rough Idle in Seville STS

    At 50,000 miles, my 2000 STS began to develop a very mild case of rough idle. Every few seconds the engine would shudder or vibrate a tiny amount, this could be seen when looking at the engine and can be felt when sitting inside the car at idle. Now, at 115,000 miles, the idle is somewhat worse, with the engine doing a slightly rougher shudder every second or so at idle. I changed the spark plugs about 1,000 miles ago, the old plugs didn't look too bad and the new plugs didn't help (and didn't worsen) the condition.

    I know there was a recall that involved new camshafts and other modifications. Is this the same condition I'm experencing? It's annoying but not a dealbreaker. Could it be something else?

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with floor shift)
    Join Date
    Jun 2004
    Location
    Woodstock Ill.
    Age
    66
    Posts
    70,459

    Re: 2000 N* Rough Idle in Seville STS

    2000+ Northstars have a rubber coupler AKA plenum between the TB and the manifold. They are known to split and cause a vacuum leak which seems to cause symptoms like yours. Spray some Brakleen around there and see if you get an RPM increase. If so, replace the "plenum".

  4. #3
    SmoothTS is offline Cadillac Owners Member
    Automobile(s): Cadillac
    Join Date
    Jan 2008
    Posts
    72

    Re: 2000 N* Rough Idle in Seville STS

    A cracked plenum is indeed the problem! Thank you!!!

  5. #4
    1998STS's Avatar
    1998STS is offline Cadillac Owners Member
    Automobile(s): 1998 Cadillac STS
    Join Date
    Jun 2005
    Location
    Muskego,Wisconsin
    Age
    38
    Posts
    20

    Thumbs down Re: 2000 N* Rough Idle in Seville STS

    I am having the same problem, only thing is I have a 1998 STS. Do 98 Caddies even have a plenum. If they do not have plenums,what else vacuum wise could be the problem. Does anyone have a picture of what a plenum looks like.Below is a list of what I have done so far. Thanks in advance.

    Plugs/Wires
    Cleaned Intake
    Cleaned EGR

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with floor shift)
    Join Date
    Jun 2004
    Location
    Woodstock Ill.
    Age
    66
    Posts
    70,459

    Re: 2000 N* Rough Idle in Seville STS

    No, the "plenum" is on the 2000+ Northstars. Check all the vacuum lines including the PCV fitting. Don't overlook the intake mounts and do not over torque them.

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS/65500mi, 2004 Ford F150 SuperCab4x4
    Join Date
    Feb 2006
    Location
    MD Eastern Shore - Kent Island
    Age
    74
    Posts
    41,611

    Re: 2000 N* Rough Idle in Seville STS

    While you're in the front of the intake manifold listening for a leaking PCV fitting, stick the stethoscope further back in there and listen for a vacuum leak around the overpressure blowoff valve in the center end of the manifold.

    Intake manifold bolt torque is only 9 ft/lb. A 2000+ "plenum" is a very short bellows arrangement with a flange plate/bolt clamp on the TB end and a hose clamp on the other (manifold) end. Plenty of pictures in here a few months ago.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting