Cracked Plenum? What's a plenum? [Archive] - GrandAmGT.com Forum

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InDaZone
03-11-2009, 09:59 PM
I just had my manifold gaskets replaced. The mechanic who did the work said my car was idling high and said I have a crack in the plenum? I needed the car that day so I guess he tried to epoxy it.

When I first start the car it idles at 1500rpms for a couple minutes before it settles real low like it's about to stall out. I also noticed a very high pitched whistle coming from somewhere. Gas mileage is terrible. My check engine light is on.... is it because of this plenum?

I plan on taking the car back next week so he can fix the plenum, but I was wondering what and where exactly is the plenum? Where can I buy one and how much it costs? Is the whistle noise coming from the crack in the plenum? Am I risking screwing up the engine permanently by driving it right now?

Sorry if that doesn't make sense, but I'm a complete idiot with cars and obviously don't know what i'm talking about. Appreciate any info anyone has.

Nick-G
03-11-2009, 10:08 PM
It's the upper intake manifold. If you have a v6 it says 3400SFI on it.

ryanbgb22
03-11-2009, 10:11 PM
I'd assume that's your problem. Where did you take it to get repaired?

InDaZone
03-11-2009, 10:39 PM
It's the upper intake manifold. If you have a v6 it says 3400SFI on it.

So the part that actually says 3400 SFI on it is what I need replaced?

Do you know where I can find one and how much they generally cost? Can't seem to google it anywhere.

I got the car fixed by some local repair shop in Buffalo, NY He seems to know his stuff, it just took him 3 days to get back to me, and then he popped this cracked plenum issue on me. Kind of makes me think he cracked it while taking it apart since i didn't have this idling problem before.

Malaclypse
03-11-2009, 10:52 PM
More than likely he did.

Having done about 100 of these intake jobs I've never broken a plenum/upper intake before. He probably torqued the corners first or something. Either that or he left a vacuum line off. Doesn't sound like the most trustworthy of mechanics out there.

3 days is a long time. The job only takes about 3 or 4 hours.

ga2001gt532
03-11-2009, 11:12 PM
http://www.grandamgt.com/forum/showthread.php?t=78241
just in time now you can get a powder coated one or go to a junk yard and get one

awfulwaffle
03-21-2009, 12:54 AM
More than likely he did.

Having done about 100 of these intake jobs I've never broken a plenum/upper intake before. He probably torqued the corners first or something. Either that or he left a vacuum line off. Doesn't sound like the most trustworthy of mechanics out there.

3 days is a long time. The job only takes about 3 or 4 hours.


Indeed it does. I've done one at work on a 3.4 Malibu in 3.5 hours, that **** ain't hard. There's a particular order in which you need to tighten the bolts in order to prevent cracking the intake manifold (of which the throttle body plenum is a part), and the guy that did the work probably overtightened some of the bolts, or like Malacalypse said he torqued the wrong bolts first. There is a bit of a problem with having a crack in your intake manifold, as the mass air flow sensor can't accurately read the flow of air coming into the engine. This causes fuel delivery issues, and your car is probably riching out. This is also why it stumbles, since the engine can't properly adjust the flow of fuel.

I say take the above and tell it to the shop owner. If it was fine before, then clearly they're responsible. You can probably get them to cover the cost of the new manifold and labor.