: Is this a cracked intake plenum? (see attached pics)

04-12-08, 07:47 PM
My 2000 Seville STS has been having a slightly rough idle and slightly increased fuel consumption now at 115,000 miles. I was told to check the Fuel Pressure Regulator (FPR) using the procedure posted in the Tech Tips section. My FPR seems to be fine. I was also told to check the intake plenum, the rubber boot connecting the throttle body to the intake manifold. The plenum looks cracked to me, but I need some expert verfication. :D Please check the photos below and let me know if this is indeed cracked. What you are looking at are some closeups of where the plenum meets the hose clamp (the clamp that attaches the plenum to the intake manifold). Thanks In Advance!!!

04-12-08, 08:24 PM
I am glad to see the pictures:thumbsup:

04-12-08, 08:39 PM
Order the plenum and a set of (new, upgraded) intake manifold gaskets.

Many, many posts in here over the past several months, with pictures and commentary, on how to do the job. An easy afternoon's work.

04-12-08, 09:31 PM
Thank you for your help, on this thread and on others! I will research, order parts, and fix this!

Is this a good time to do some other maintenance? I was thinking I could also clean the TB and possibly inspect the EGR valve and maybe the MAF sensor at the same time. What do you think? Is there anything else I should check out while I'm working under the hood? My car has 115,000 miles and I changed the plugs and plug boots about 500 miles ago. Aside from oil changes, air filter, tires, and battery, nothing else has been changed or worked on.

Thank you again! You folks, and this whole forum, are the best! :bouncy:

04-14-08, 12:40 AM
Yes, pretty good catch picture wise.

Typically the crack is on the bottom. Dont know why..maybe the nasty goo's from PCV / EGR valves have a place to hid.

Yes, the intake has to come off to replace this $25 rubber coupler. Good news is in most cases you can reuse the intake gasket.

It's a dry intake, couple hour job. No coolant issues. Pretty fast job.

BTW..getting any codes? Lean banks?

Logan Diagnostic LLC

04-14-08, 08:24 PM

I'm having a slightly rough idle issue too. Mine feels like a very slight miss. Could you please describe your rough idle. How were your Ltrims at idle?

09-05-08, 08:25 PM
Can you re post the plenum pics. They are not showing up on my screen?

09-05-08, 08:39 PM
I don't see any either.

09-05-08, 09:59 PM
...........doubt he will bump a 5 month old thread that has been fixed......The pics showed a typical 2000+ cracked plenum at the bottom of the bellows and at the s/s ring clamp.

Many, many more such pics here, in Seville and Deville.

09-05-08, 10:48 PM
Sub, why do you see the pics and we can't?

09-06-08, 11:00 AM
I did not see the pictures this time around: I remember replying to his question and looked for my post in which I HAD seen the pictures......but I have not seen hide nor hair of the OP since then.............

Logandiagnostic also seems to have seen the pics referred to in the first post.

As far as MillerBlack's question, a dental mirror or small mechanic's mirror and flashlight will sometimes show the crack(s) if you look at the bottom of the plenum bellows. The edges of the crack may be shiny and oily.

The pics below were taken from a post last year concerning a 2001 DHS plenum. Click and scroll in.......

07-18-12, 09:54 AM
I would like to see these pics

07-18-12, 11:58 AM
I would like to see these pics

Why ??? To dredge up a 4 year old thread and supply no amplifying info seems a bit odd. There are threads and far, far, more recent pictures of this problem posted in 2012.

If you believe that you have a leaking plenum (vacuum leak), Google something like "cadillac forums northstar intake plenum leak"

For pictures of the plenum and the associated intake manifold and equipment, look through my albums - Up in "Community", Albums.

12-03-12, 07:28 PM
I am having some idle issues when cold, had 2 codes po171 and po174, bank 1 lean bank 2 lean, I was told it was the plenum, or is it just the coupler, I am a little confused,thanks

12-03-12, 10:42 PM
It's the "plenum". On the Northstar the rubber coupler is called the plenum. :noidea: GM named it, not me. I think my manual more accurately calls it the "plenum duct". Whatever you call it, THAT'S your problem.

12-04-12, 08:23 AM
I am having some idle issues when cold, had 2 codes po171 and po174, bank 1 lean bank 2 lean, I was told it was the plenum, or is it just the coupler, I am a little confused,thanks

Post #13, last sentence - or click my username, open the profile. left column, lower part. 2 albums, 6 pages of parts and service pictures and diagrams for the 2000 and later Northstar and cars.

12-15-12, 11:49 AM
Thanks for the info, found the rubber plenum with a big crack. Had a friend replace it for me, I read a few of the replacment procedures, my friend didnt have to remove the fuek rail save some time. Thanks again for the help.