: Rough Idle Question For Ewill3rd



Ranger
08-10-08, 04:44 PM
I have noticed a rough idle on cold starts. It lasts for about 40 seconds (till the A.I.R. pump shuts down and the idle drops). I assume that it is not a problem, is normal, and I am not concerned. I just don't understand what causes it. Doesn't the A.I.R. pump simply put fresh air into the exhaust manifold? How could that cause a rough idle. No DTC's. Splain this to me. I'm baffled. :confused:

AJxtcman
08-10-08, 10:26 PM
Is it kind of a pulsing and rumbling noise?

Ranger
08-10-08, 10:29 PM
Nope. No sound at all AJ. Just feels like a misfire.

AJxtcman
08-11-08, 08:06 AM
Nope. No sound at all AJ. Just feels like a misfire.

Very Normal.

I will get you some information on it.

You are 100% sure it is not raw fuel igniting it the exhaust system?

When the AIR is on the O2 data is ignored.

This only occurs in the first 1 minute of run time and with the AIR running only Correct?

ewill3rd
08-11-08, 08:31 AM
It could be anything from normal to head gaskets.

Only does this on a COLD start?

AIR should have no effect on idle quality, it does just pump fresh air into the exhaust.
We'll see what AJ comes up with.

AJxtcman
08-11-08, 08:47 AM
It could be anything from normal to head gaskets.

Only does this on a COLD start?

AIR should have no effect on idle quality, it does just pump fresh air into the exhaust.
We'll see what AJ comes up with.

Take a look at this
PIP3546A

I know it does not fit this car.
I have noticed it on the newer cars and since I have been listening for it I have noticed it on older cars.

I will dig around and see what I come up with for his car

ewill3rd
08-11-08, 10:02 AM
That looks like the condition I hear on the new style DTS, it says '06-'07.
Those all do that.
I think he's talking more about a misfire sensation than a noise.

Ranger
08-11-08, 04:57 PM
Yeah, no noise at all. Temp gauge is rock solid at 12:00. AIR pump stays on for 40 seconds. That is the only time I feel this rough idle (cold start). After 40 seconds, the pump must go off as that is when the idle drops from 1200 to about 800 and then smooths out. I have not checked the FPR, but mileage is averaging 24.7.

eldorado1
08-11-08, 07:22 PM
I don't know the nuances of the stock caddy system, at least not a 2003, but it could just be a coincidence that the air pump is on while you have a rough idle. If the evap canister purge lines has a vacuum leak, it could be drawing in air instead of gas fumes, causing a lean misfire. The purge typically occurs during the first few seconds after startup at idle, so I would put it high on the suspects list.

Ranger
08-11-08, 08:30 PM
If the EVAP system had a leak it would set a DTC. I had no DTC's except for 1 or 2 pesky "U" codes.

eldorado1
08-11-08, 10:52 PM
codes are a crutch for people who don't think outside the box. :cool2:

I've seen cars set MAP codes when the TPS was faulty, and badly misfiring cars with no codes. It can only set a code when something falls outside of a predetermined range, nevermind that "normal" could be a narrow window inside that range for your particular engine. It's better to have no codes than false codes, as they say.

Hit the misfiring troubleshooting tree.

AJxtcman
08-12-08, 07:17 AM
New calibration to correct the EST control circuit in the PCM from turning off spark intermittently which causes multiple misfire events, possibly resulting in a damaged catalytic converter indicated by DTC P0420.
2003 Cadillac DeVille 3U100001 to 3U216368


I am still leaning towards the AIR igniting raw fuel in the exhaust manifold and disturbing the charge in the cylinder. It acts like a misfire.
E-10 could have an effect on this also.

I have been seeing a lot of this in the last few years, but I became tuned into it because of the issue with the 06 & 07 DTS that is a normal condition.

We know that E-10+ is more volatile.

http://www.epa.gov/otaq/rfg/images/rfgmap-v2-500.gif

Ranger
08-12-08, 04:53 PM
Well I have been running E10 for decades now and never had a problem yet. Ran it on this car since I've had it (2 years now) with no problems. Checked the FPR last night when I got home. No leaky. Just to clarify, it is a very, very minor roughness.

ewill3rd
08-12-08, 08:35 PM
You might run some TEC through it Ranger.
It could just be a little carbon buildup.

Ranger
08-12-08, 09:34 PM
Not to doubt you Bill, but why only for the first 40 seconds during high idle? FWIW my '97 had 106K on it when I sold it and never put anything but gas in the tank. Never had a problem. Not that this is a problem. I was just curious more than anything. Maybe I'll just ignore it. If it IS a problem, I'm sure it will get worse and let me know. I just thought perhaps it was something that you had seen before.

ewill3rd
08-13-08, 06:43 AM
Sometimes the carbon buildup in the cylinders will act like a sponge during the first few seconds of startup.
It can soak up fuel and lean out the clinder a bit. Not to say that is what is happening but you could have a sticky valve or something.
Usually running a couple cans of TEC through the top end can clean up some carbon buildup. Not being a real engine guy I don't see a whole lot of it, but I seem to recall hearing that this engine does have carbon issues.
We do a lot of TEC treatments, mainly for noises on startup or small hiccups like what you have.

Have you ever done it before? I have a trick that works pretty well and it doesn't even take that long.
You have to be sure your neighbors aren't watching because it turns your car into a rolling smoke bomb for about 10 minutes. :lol:

AJxtcman
08-13-08, 07:09 AM
I will try to video one that has a custom exhaust system. This allow you to hear the AIR system igniting the raw fuel.

Ranger says it has been doing it since day 1 and it is only when the AIR is on.

Highline's car will "throw flames out the pipes" when the AIR is on it you work the throttle just right.

Again I have been keyed into it after the DTS came out and the car is way worse.

Ranger
08-13-08, 03:21 PM
I will try to video one that has a custom exhaust system. This allow you to hear the AIR system igniting the raw fuel.

Ranger says it has been doing it since day 1 and it is only when the AIR is on.

Highline's car will "throw flames out the pipes" when the AIR is on it you work the throttle just right.

Again I have been keyed into it after the DTS came out and the car is way worse.
No I said I have been using E10 since day 1. I am not positive how long this rough idle has been going on, but I don't recall it was from the start. As I said though, it is very, very minor. Again, I'm not going to worry about it for now.

AJxtcman
08-13-08, 06:51 PM
No I said I have been using E10 since day 1. I am not positive how long this rough idle has been going on, but I don't recall it was from the start. As I said though, it is very, very minor. Again, I'm not going to worry about it for now.

I see that I misread something again :nono:

I shouls have video'd a couple of cars today :histeric:
Then you can compare it

AJxtcman
08-13-08, 06:54 PM
Listen to the exhaust when this occurs. Back at the tail pipes.

90devilleguy
08-13-08, 10:32 PM
Ranger you are not alone, my 02 SLS does the same thing. I think it's normal...even after i had to replace one of the ign coil modules and all the spark plugs with the OEM plantiums, it still does the rough idle during warm up. And it's seriously only during a cold start, cause i noticed that if I start the car, let it idle down then drive it for like 5 minutes(to the bank let's say) then shut off the car, take about 5 minutes in the bank, get backin the car and start it up it will idle high and the AIR will kick on but the car doesn't seem to idle rough.......So i'm thinking it's when it sits overnight and you start it the next day all the crap builds up and then the car trys to clean it out on start but it's cold so it's gonna run rough during the initial warm up procedure.

That's my philosopy.