: Extremely Rough Idle... Cracked Intake Manifold?



Playdrv4me
01-10-06, 08:23 PM
I just bought a 2001 SLS on the cheap and one of the problems the car had was an extremely rough Idle which literally shakes the whole engine when its bad enough.

The car rides just fine on the highway once throttle is applied and actually made it the 1500 miles down to FL from Kansas in a matter of 24 hours with no major problems except for an occasional bucking, jerking problem at cruising speed that felt more like a Throttle position sesnor issue than a tranny issue or anything like that. The car has 98000 miles.

The car is throwing codes for MAF Sensor Performance "P0101" and two codes for Fuel Trim System Lean (P0171 and P0174). The other significant sign of a problem is an extremely loud hissing noise coming from the engine bay when the hood is opened. I sprayed some TB cleaner on the engine, and it appears the hissing is coming from the junction between the TB and the Intake Manifold, as this is where the engine idle speed becomes rapid when I spray the TB cleaner right on that center area. Unfortunately, its pretty much anywhere in that area rather than one concentrated spot.

I think this is enough info to gain some sort of insight from the experts, any ideas? Ive been quoted 500.00 for an intake manifold replacement if it is indeed cracked. By the way, who is the idiot that came up with PLASTIC intake manifolds? I dunno, something about plastic as a major compoenent of my engine doesnt sit right.

Thanks
Ian.

eldorado1
01-10-06, 08:43 PM
I don't remember the exact details of the 2000, but I believe there's a rubber tube between the intake and the throttle body/water crossover. It would make sense for them to use hose clamps on either end. The good news with the 2000, is that you can take off the manifold with practically no work... I would look into the hose clamps being loose first, it's unlikely you have a crack.

Ranger
01-10-06, 10:16 PM
I agree. If there are not hose clamps, then there should be a gasket or "O" ring. I would suspect something like that much sooner than a cracked intake.

Playdrv4me
01-10-06, 10:43 PM
Interesting... very interesting indeed. The main reason I hopped on the Manifold cracked bandwagon was because Stoney had come to that conclusion after reading some of my initial posts when I was buying the car originally. However some of my information was mixed up. I was the told the car needed something resealed, they were talking about the oil issue, not anything to do with the Intake manifold.

zonie77
01-10-06, 10:47 PM
Manifolds do occassionally crack although I've heard it on Ford's and Chevys. It's fairly easy so take off and inspect. I think that's the next step.

Congratulations on buying the Caddy!

eldorado1
01-10-06, 11:40 PM
Well I cracked mine, but it was because I overtightened the bolts. Oil on the bolt threads, bad torque readings does make.

Eldyfig
02-17-06, 09:32 PM
Eldorado1, did you hear the intake crack while you were tightening it or did you finally notice when you removed it? My intake seal was leaking on the front right of the engine. I checked the torque and it was about 5 ft/lb. I went ahead and tightened it to 7.5. No leak for some time until the weather got fairly cold. I rechecked the torque and tightened it down just a tad more. I was figuring the seal was crushing, that being the reason for torque loss.

The new intake seals from Rockauto arrived today. After reading this post, I hope I haven't cracked the intake. At the present moment the idle is rough, but there isn't any whistle like before. I will be replacing the seals tomorrow.

eldorado1
02-17-06, 09:46 PM
Well I didn't crack the manifold enough for vacuum to escape (I don't *think*, it's possible because of some problems I had been having at the time)

Basically I crushed the manifold "standoffs" I guess you could call them. The cylindrical part the bolt slides through mushroomed and split. This is on a plastic intake btw, your profile says you have a 94... I doubt you'd have a problem with a cracked manifold there. Possibly the phenolic spacer(s) cracked...

davesdeville
02-18-06, 08:05 AM
If you suspect a vacuum leak (IE cracked manifold or otherwise) get a propane torch, don't light it and turn it on, aim it at where you think the crack is. If the rough idle smooths out you found the problem...

Eldyfig
02-18-06, 11:11 AM
This is on a plastic intake btw, your profile says you have a 94... I doubt you'd have a problem with a cracked manifold there. Possibly the phenolic spacer(s) cracked...

You are right. Thanks.

I found the location of the main leak with my stethoscope. It was already whistling. When I put the probe down near the spacer near the front of the engine, my ears received a good tingle.

I am going outside in the next few minutes to start the job.

ewill3rd
02-19-06, 05:42 PM
Hey play, you need to replace the "plenum" if you haven't already.
It's not the intake that is cracked.
The plenum has a boot that attaches to the crossover/throttle body with three screws and then you just loosen the hose clamp.
You will have to remove the intake and I recommend replacing the intake seals that seal the intake to the cylinder heads. Otherwise you might have another leak soon.
It happens quite often.

HTH.

Eldyfig
02-22-06, 05:14 PM
Finished my intake seals this past weekend. New seals fixed my leak up good.

Had alot of crap in the egr valleys. That is all clean now. Mine is running smooth. I am very pleased.

The job in all is not hard at all.

OffThaHorseCEO
12-21-06, 09:51 PM
these are the exact symptoms mine has, down to the rubber boot hissing

OffThaHorseCEO
12-22-06, 12:18 AM
so what was the fix? and where cani get a replacement for that boot?

Ranger
12-22-06, 01:10 AM
The fix is to replace the rubber coupler. Try http://www.gmotors.com

OffThaHorseCEO
12-22-06, 03:38 PM
damn, 5 minutes response turnaround time

thanks for the link!!!

OffThaHorseCEO
01-10-07, 09:03 PM
Hey play, you need to replace the "plenum" if you haven't already.
It's not the intake that is cracked.
The plenum has a boot that attaches to the crossover/throttle body with three screws and then you just loosen the hose clamp.
You will have to remove the intake and I recommend replacing the intake seals that seal the intake to the cylinder heads. Otherwise you might have another leak soon.
It happens quite often.

HTH.

so i just received my rubber boot, i need to r and r the intake manifold while swappin this out?

i might need to get my local mechanic to do it for me

ewill3rd
01-11-07, 06:59 AM
Yes you need to remove the intake.
It's really quite easy, but if you don't feel comfortable tackling it, you would probably be better off having someone do it for you.
Be sure to replace the 8 blue seals on the bottom of the intake or you might end up with another leak.

OffThaHorseCEO
01-11-07, 06:45 PM
well, im not afraid to admit im not comfortable doin it hehe, i mean i can do the basic oil change spark plug swap and i can do radios speakers etc, but this involves engine internals, so im kinda uncomfortable with it.

btw where can i get those replacement blue seals? and how long does this procedure take (im tryin to see how much a mechanic should charge me...or maybe maybe i can try it myself)

CADILLAC TECH12
01-14-07, 11:10 PM
171 and 174 are fuel trim lean codes, which means you are getting to much air into the system. the most commmon proble is the intake manifold plenum boot. it is a rubber boot that that attaches them manifold to the aluminum crossover. it is pretty easy to diagnose if you have a can of b-12 or carb cleaner spray the boot while the engine is on, and if there is a leak the engine will start to idle funny or die spray the boot and the edges of the manifold. it is easy to replaced the boot remove the manifold replace the boot and the 8 manifold seals. be sure not to allow anything to fall into the intake openings on the heads and not to loose any injectors o-rings. i hope this helps