: AC & Intake

05-26-08, 08:25 PM
2001 Deville
I need some assistance with 2 problems that I am currently having if anyone can help. My first problem is my AC. Last year I paid Firestone almost $500 to replace what I think was an actuator dealing with the blend door. Can't remember the specifics but basically only the passenger side was cold til I had that work done. Worked fine after that. This was done June last year. Now I have the same issue again. Come to find out that part only had a 6 month warranty brand new. I'm not trying to shell out $500 again for the same part again. I'd rather do it myself for that but I hear AC isn't fun to deal with.

Next I now have a nasty rough idle whether parked or in drive. I checked the code as my engine light came on and cleared it and it came back. I know its not a misfire since none of the codes state that, however it has I think 2 codes that related to some kind of fuel trim issue. I googled some on it and it says something about a intake plenum. No idea what that is or where it goes. I'm more into doing things that are simple fixes to my car that aren't extremely technical in nature that require an actual mechanic. Just saved myself over $500 for a window regulator at the dealership by spending $45 on Partstrain.com and doing it myself. Gas money is a must these days so if anyone with the knowledge and can point me in the right direction would greatly be appreciated.

05-26-08, 08:39 PM
Start off by adding your year and model to you profile. It will make a difference in some of the answers.

Differential temperatures between the left and right A/C ducts is a classic symptom of low refrigerant on a dual zone system. You probably didn't need the actuator unless there was a DTC indicating so. Have the refrigerant serviced or add a can yourself.

The plenum you speak of is only on the 2000+ engines. It is the rubber coupler between the TB and the intake manifold. It is a pretty common failure and will cause the symptoms you describe.

06-17-08, 02:19 AM
Ok i can now close this post. I had a looked at about 2 weeks ago then had to go on the water for awhile but I'm back. They found that my intake manifold is cracked so that has to be replaced before my heads go bad too. Looking to do that this wkend. $700 parts and labor. Also found that I need the fuel system serviced for build up for $300. Wonderful year. The AC is still a mystery however for some reason its all of a sudden working but they couldn't find out why it wasn't working but whatever they did has me feeling comfortable now. Didn't even get charged for that. Ranger thanks for the assistance. I will prolly be pinging u for further issues and upgrades that I'm thinking about doing to my baby.

06-17-08, 10:58 AM
Wait a minute. I smell a rat. Cracked intake manifold? Fuel system serviced for build up? The problem is the "plenum" as I mentioned above, NOT the manifold itself. It is a cheap fix. The fuel thing sounds like a money maker to me. I think you are being taken for a ride.

06-17-08, 12:36 PM

I never heard of a cracked Northstar intake manifold. Maybe a leak in the backfire valve, more often a plenum in the later Northstars.

06-17-08, 01:56 PM
:yeah:.......Plenum. The manifold bolt torque is only 9 ft/lb. Not very tight. Also check the overpressure valve and PCV fitting in the manifold. Plastic vacuum lines can crack.

Never heard of fuel system service for buildup (of what?).

06-17-08, 07:03 PM
Second all of the above. You're getting ripped BAD. Find another mechanic!

06-21-08, 07:21 AM
Yea i was thinking the same thing about that issue because they took almost 3 days to even tell me anything saying that their mechanic that works on cadillac wasnt around. this is the first time I've had a problem with Firestone. I took the cover off to look for myself to see if there was any damage to the manifold itself and didnt see anything besides the fact that it doesnt even appear to have been looked at since its dusty and no fingerprints whatsoever. The black piece beneath the silver cover is the manifold itself? I looked at the piece for the air intake from the filter to the manifold and it appears intact as far as i can see. I have a friend with a cts who knows a mechanic that works for the local cadillac dealership so i will see what he can do. This northstar is so complicated, expensive and more expensive but i love em. I heard about the lines going bad too. I'll see if he can look at everything for me. Try to get this done before my ship goes out to sea again. I'll keep u guys updated.

06-21-08, 07:28 AM
Yep, the black twisted-looking thing is the intake manifold.......individual tuned port runners. The hold-down bolt torque is 9 ft/lb. Ask the mechanic to check for a vacuum leak under the rubber connection (plenum) between the manifold and throttlebody.

06-21-08, 08:16 AM
One thing I forgot to mention. I know when the car cold starts it has that vacuum systems that makes it warm up quicker. When it does that my car shows no symtoms but as soon as it cuts off you began to notice the idle. Giving you guys as much info as I can.

06-21-08, 08:24 AM
OK.....The idle speed increase during the first 15 - 20 seconds of warmup is controlled by the ISC (Idle Speed Control), TPS (Throttle Position Sensor), and mixture control from the PCM.

You may be in for something as simple as a throttlebody and idle air passage cleaning. That's a process detailed many times in here and a bit more in Seville/Deville, and will most definitely affect idle quality.

06-21-08, 09:03 AM
So that would cause it to rough idle like that. I mean when I'm at a light the engine shakes the hell outta my car sometimes. It's wierd too because one day it won't be so bad and the next it's like those cars in the movies and jerking hard til I give it some gas and it'll stop til I release it. Sometimes I just sit in neutral til the light changes. Sucks. Is that what's causing the engine light to come on? It's fuel trim thing. 2 different codes. I've cleared the light twice and drive around the block to see what happens and it comes right back on.

06-21-08, 09:56 AM
Have you checked the plenum? NOT the intake manifold, but the rubber coupler between the TB and the manifold. Spray some Brakleen near the underside of it while idling and see if the RPM increases.

10-24-08, 10:13 PM
Like to say thanks to Ranger and everyone else who helped me with my baby but unfortunately she has been sent to Caddy heaven do to her being totaled in an accident, but she has a successor. I now am proud to be the owner of a 2006 DTS, Blk on Blk in Blk. Thread is now dead.
Pece....not a typo