Why does my car run rough when idle?

Tiny
BBOLDEN
  • 2004 CADILLAC SRX
  • 120,000 MILES

After approx. 30 mins of driving my car begins to run rough but only when I'm stopped. It also makes a rattling noise. Check engine light is not on. What could this be?
Thanks for your help

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Tuesday, January 3rd, 2012 AT 12:23 AM

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Tiny
CJ MEDEVAC
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AN ALMOST FREE THING YOU COULD DO IS REMOVE AND CLEAN THE IAC

IT CONTROLS THE IDLE, IF IT MAKES ANY DIFFERENCE, THIS MAY EVEN JUSTIFY REPLACING IT. IT'S MOST LIKELY BEEN YOUR PAL FOR 120,000 MILES UP UNTIL NOW

IT IS ON MOST VEHICLES, AN EZ TO DO, CAN YOU HANDLE IT?

THE MEDIC

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Tuesday, January 3rd, 2012 AT 12:37 AM
Tiny
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Thank you so much.I surely cant handle it. But I will try to find someone that can. Thanks again

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Tuesday, January 3rd, 2012 AT 12:45 AM
Tiny
CJ MEDEVAC
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COME ON!!!!

I'LL HELP YOU!

IT IS SO EZ---IT WILL TAKE LESS THAN 30 MINUTES W/ A CAST ON YOUR DOMINATE ARM!

RESPOND AND I WILL CONTINUE WITH THE PROCESS OF HOW

I HAD SAME ISSUE WITH WIFEYS FORD ESCAPE--I TOOK 3 PICS

2 BOLTS---SEE MY LINK--WHERE I ANSWERED ANOTHER FELLER (JAN 9)

http://www.2carpros.com/questions/2006-ford-f-250-truck-not-running-great

EVEN IF THIS AIN'T THE PROBLEM NOTHING IS HURT! AND THIS MIGHT BE ELIMINATED AS A FACTOR.

WAITIN' ON YOU

THE MEDIC

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Tuesday, January 3rd, 2012 AT 1:06 AM
Tiny
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Well you make it sound quite easy. So I guess I could give it a try. Would you happen to have any pictures of where the IAC is located?

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Tuesday, January 3rd, 2012 AT 1:14 AM
Tiny
CJ MEDEVAC
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WILL TAKE ME LONGER TO GET STUFF READY--THAN FOR YOU TO TACKLE IT

GIVE ME A FEW

THE MEDIC

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Tuesday, January 3rd, 2012 AT 1:18 AM
Tiny
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Thanks much.I do appreciate it.

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Tuesday, January 3rd, 2012 AT 2:02 AM
Tiny
CJ MEDEVAC
  • EXPERT
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OK---I HAVE RAN INTO A GLITCH

PRIOR TO RESPONDING TO YOUR QUESTION I WENT TO A RESOURCE I USE FREQUENTLY TO INSURE YOUR VEHICLE HAD A IDLE AIR CONTROL (IAC)

THE "NO CHECK ENGINE LIGHT" MADE ME THINK OF MY DIAGNOSIS W/ OUR FORD ESCAPE ISSUE

SEEMS WHEN I WENT BACK GET MORE INFO, I INITIALLY ENTERED INCORRECT INFO

SO.I'M SORTA STUCK

I AM ABOUT TO FIND ANOTHER EXPERT TO AID YOU.I DO "MY THING" BEST WITH JEEP CJs

STICK AROUND, SOMEONE WILL TAKE OVER SOON--STILL MAY BE EZ!--- I AM SORRY

THE MEDIC

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Tuesday, January 3rd, 2012 AT 2:13 AM
Tiny
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No problem.I appreciate you taking the time out to respond.

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Tuesday, January 3rd, 2012 AT 2:41 AM
Tiny
CARADIODOC
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  • 27,235 POSTS

Hi guys. Any additional symptoms or observations would be helpful, but here's something to consider that only pertains to GM vehicles with higher mileage. It has to do with mismatched flow rates of the injectors. Chrysler buys their injectors from Bosch in matched sets and problems with them are just about unheard of. They last well beyond the life of the car. GM grabs a handful of injectors out of a huge bin and throws them in an engine with no regard to matching their flow rates. As the engine ages and the injectors begin to show a little wear, some will not flow as much fuel as the rest resulting in one or two cylinders running lean. The unburned oxygen is detected, but the computer doesn't realize that it's being caused by only a few cylinders, so it asks for more fuel from all of the injectors, even those that are flowing too much fuel already. This can be a hard one to figure out because there isn't exactly a defect that can be easily diagnosed and there won't be a stored diagnostic fault code. Now that it has become more widely known, there is a company that specializes in rebuilding injectors and GM injectors are their most popular product. They are flow-matched and sold only in matched sets. Many owners claim their engines never ran so smoothly since the car was new.

Besides the lean misfire, (which should be detected by the Engine Computer on '96 and newer cars), the computer will be constantly trying to add fuel and that can result in an excessively rich condition. The computer might be able to add enough fuel so the lean cylinders have the correct mixture but the rest will be too rich. Oxygen sensors don't detect unburned fuel, just unburned oxygen. Part of the strategy in adjusting the mixture is to run it too lean a couple of times per second and to run it rich other times. The computer expects the oxygen sensors to detect a specific amount of oxygen from all of the cylinders. To achieve that, it will likely not add enough fuel over the long term to keep the lean cylinders happy. A clue to finding this is by watching the long and short-term fuel trim numbers on a scanner that displays live data. If all of the numbers are positive, the computer is requesting more fuel beyond the pre-programmed values from the factory. At the same time, the system will be listed as "lean" for longer periods of time than it is "rich". It should switch a couple of times per second if all the injectors are flowing equally.

Since the Check Engine light is not on, there is likely no stored diagnostic fault code related to a misfire. You might consider other causes of a rough running engine. GM has more than their share of worn engine mounts. That can allow metal parts to touch and transmit normal engine vibration into the passenger compartment. Bent metal exhaust hangers can do that too. They always have some type of rubber insulator between the two parts of the assembly to isolate vibration.

Also consider low fuel pressure. Chrysler pumps will fail to start up when they're worn from high mileage, but once they start running, they never quit while you're driving. GM pumps are exactly the opposite. They will almost always start up but will stop working unexpectedly and let you sit on the side of the highway. The system is very picky about precise fuel pressure. Most cars will run fine with slightly low fuel pressure but on some GM engines, 2 pounds low can cause misfires from fuel failing to spray from an injector. The low pressure can develop after the pump gets warm.

Another cause that is strictly a GM problem is the generator, and it's a big one. They went from the second best generator design to the world's worst pile starting with the '87 models. Due to their design, they develop huge voltage spikes that can destroy the internal diodes and voltage regulator, and they can interfere with computer sensor signals. It is real common to go through four to six generators in the life of the car. The way to reduce the number of repeat failures is to replace the perfectly good battery at the same time the generator is replaced, (or before it goes bad). As they age, even though they start the engine just fine, they lose their ability to dampen and absorb those voltage spikes. When one of the six internal diodes fails, the generator's output capacity is cut to one third of normal. That can be barely enough to run the fuel pump, head lights, and all of the very many computers with nothing left over to recharge the battery. System voltage will go low and computers can not handle low voltage.

Those voltage spikes cause current spikes which radiate out magnetically from the wiring into sensor wiring. Beside being confused when running on low voltage, those spikes show up as glitches from sensors and will confuse computers even more. Even when system voltage is not low, those spikes can affect computers. A simple test to see if the generator is responsible for a rough running engine is to unplug the small plug on the back. If the engine smooths out, suspect the generator and battery.

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Tuesday, January 3rd, 2012 AT 7:59 AM
Tiny
FACTORYJACK
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Start basic, if this is a 3.6L, check the oil level. There is no oil level detection on this powertrain, and when it reaches 4 quarts low it starts to have issues. Noise, misfires, etc, most commonly at idle.

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Tuesday, January 3rd, 2012 AT 4:28 PM
Tiny
SATURNTECH9
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Even though the check engine light isnt on you shopuld still take it to a auto parts store and have them scan it for codes. If you have any please post your exact code nubers not code descriptions. Also is this a v6 or v8?

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Wednesday, January 4th, 2012 AT 12:48 AM
Tiny
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Thanks all.I will check oil and have codes pulled tomorrow and post them and it is a V6. Thanks again

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Wednesday, January 4th, 2012 AT 4:58 AM
Tiny
SATURNTECH9
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Alright keep us posted.

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Wednesday, January 4th, 2012 AT 5:02 AM
Tiny
ABATTISTESSA
  • MEMBER

Hi Guys - I have a very similar problem. And I would like to avoid taking my 2004 SRX into the shop if possible. The symptoms are similar in that as the engine gets warmer and is ideling it gets roughfer and roughfer. Meaning more vibration.

Does anyone have a check list of plausible causes?

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Wednesday, February 8th, 2012 AT 5:39 AM
Tiny
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Hi All,
I took it in for computer diagnostics and this is what they found codes po304, po301, po303, defective ignition coils 1 and 3 broken connector for throttle body, defective cam shaft actuators b1 1 and 3 spark plugs- intake plenum gaskets- cam shaft solenoids. Its in for repair now.I hope this helps

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Wednesday, February 8th, 2012 AT 2:21 PM
Tiny
ABATTISTESSA
  • MEMBER

WOW - How much did they say it would all cost? :(

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Wednesday, February 8th, 2012 AT 8:51 PM
Tiny
CARADIODOC
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Abattistessa, you're doing yourself a disservice by piggybacking on this thread for a couple of reasons. First of all, there are a lot of really smart experts here who are not going to even see your problem or be able to reply because only those of us who replied previously will get an automated e-mail directing us back here when any reply is posted. You're losing the chance to have your question read by those other people.

Second, there are dozens, if not hundreds of different things that can cause your symptoms and it is very rare for two different cars to have the same causes for their problems, especially when it's something uncommon like a "broken connector". You're incorrectly assuming your car has the same causes for the problem and will cost the same amount to fix. That very often leads to the assumption your mechanic is ripping you off when he "finds" something else that is going to cost more to fix.

You need to start a new thread so everyone can read it and have a chance to help. Also, please understand that when you're asking about engine performance problems, we really need to know the engine size. They often use different systems and different parts that commonly fail. They will have different symptoms and require different testing methods to narrow down the cause of the problem.

For the most accurate answer, please include all the details and observations as possible. You started that already but you might include things like reduced fuel mileage, black smoke from the tail pipe, reduced power, ... Things like that. With an answer tailored specifically to your car and problem, you'll be better prepared when you visit your mechanic of if you choose to try to fix it yourself.

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Wednesday, February 8th, 2012 AT 9:18 PM
Tiny
ABATTISTESSA
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Caradiodoc: Thank you! This is my first time ever using a forum and its proving to be very useful - I will begin a new thread ASAP and add as much detail as possible.

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Wednesday, February 8th, 2012 AT 9:39 PM
Tiny
FACTORYJACK
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What was said to be causing the rattling noise? It would seem to me that if there were camshaft actuator solenoids that were 'bad', there would be codes other than/in addition to the p0301-p0304. Did you ever check the oil, it is not stated. If you did not, then it sounds like you may have paid a hefty price for someone to add 4 quarts of oil. Think back to when was the last time the oil was changed, and how many miles were put on the vehicle in between either the change, or a checking of the level.

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Thursday, February 9th, 2012 AT 3:41 AM
Tiny
BBOLDEN
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Ok here's the latest. The cam solenoids were ok. But it returned a code of p0016 timing chain may have jumped is what it said, because this place doesnt do this type of repair they didnt fix anything. Now check engine light is on and codes come back for misfires on cylinders 2 and 3 and random misfires. So I have no clue what to do next besides buy a new car:(

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Friday, February 10th, 2012 AT 1:52 AM

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