Sub Idle when stopping.

[bigbuzuki]

I have noticed that every time I come to a stop in my vehicle, the idle slightly dips below the normal idle speed causing the car to shudder and then the idle recovers back to normal.

I have had all 8 coils replaced recently but the car still exhibits this sub idle routine when I am coming to a stop with the transmission in drive and foot on the brake.

Is this normal behaviour on anyone elses Cayenne?

This linked post describes the same symptom.

Click here

Any techs out there care to comment on how this torque bracket can cause the idle to drop. :help:

I would appreciate if anyone else can confirm or deny this behaviour on their Cayenne as the car is currently in the workshop for a service and would be a good time to get this fixed.

Thanks.

Edited December 5, 2009 by bigbuzuki

[wvicary]

Clean the throttle bodies and should clear things up.

[motec]

How many seconds does the engine run rough?

[bigbuzuki]

How many seconds does the engine run rough?

Its only for about one second just as the car pulls up to a stop, the motor shudders as the revs dip below nominal and then recovers. The dealer says its normal but it just doesn't feel right.

Any other Cayenne owners experience this?

[motec]

I think it's normal, mine does the same thing. You can also feel it as the engine revs just slightly over idle rpm.

Looking with a scan tool it seems the timing becomes quite advanced over idle levels and the secondary air operates which is the cause of the rough running

feel.

[avmedco]

I think it's normal, mine does the same thing. You can also feel it as the engine revs just slightly over idle rpm.

Looking with a scan tool it seems the timing becomes quite advanced over idle levels and the secondary air operates which is the cause of the rough running

feel.

I brought mine to the dealership (04 Cayenne turbo) for the same thing. They said nothing was found. The plugs and coils had been done already. However I noticed the brand new loaner cayenne (non-turbo) did exactly they same thing. So I can only assume it's nomal but annoying

[darrinsmith]

Hi

My 03 turbo starting doing this after I switched to K&N filters.

Annnoying but appears harmless.

Does not generate any error codes in the ECU.

Cheers

DS

[poleposition]

Hi guys,

I've just bought a Cayenne Turbo myself, and it doeas the exact same thing, I've inquired, and it seems to be normal :)

On thursday I will drop it to the dealer for usual service operations, do you have any other sugestions, on what to change/check ?

I will do: oil, filters, transmission fluids, coils, plugs, cleaning the throttle bodies, changing the coolant, brake pads.

Edited December 15, 2009 by poleposition

[wvicary]

I don't think a low idle and shudder is normal. I have driven many Cayennes and have not had this problem.

[SWFLHOMES]

Mine does it. It feels more like a low RPM transmission shift from 3rd to 2nd. It's a very slight shudder.

[spd64]

Mine does the same thing and so did most of the Cayennes I test drove before I purchased mine. I would assume it to be normal behavior but I have noticed it is less severe in colder weather and also when the car has just been started up and the engine is still cold.

[wvicary]

Perhaps my definition of a shudder and low idle are more severe then the norm.

[shastamonk]

My 04 S just started doing this at 105k mi. It never did this untill recently. No way is this "Normal"! A $75 K car is normal to studder when you come to a stop?! I don't think so. Why didn't it do it when the car was new? Perhaps whoever is the one saying this is normal can explain what the car is actualy doing???? Mine happens more and harder the hotter the car and outside temp are. I'm thinking fuel pump, or drive tran myself.

Regards,

Scott

[bigbuzuki]

I had the service tech go for a test ride in my car and he witnessed the sub idle tremor as we were coming to a stop.

His explanation was that it is the transfer case / transmission holding gear which subsequently loads the engine at low speed prior to coming to a stop. Once the gear is released the idle recovers. All this happens in less than a second.

He said it was part of the self learning characteristics of the drive system and alot of city type driving will cause the vehicle to behave this way.

He didn't consider this as a fault due to no fault codes being logged and the tremor experienced during the sub idle he considered negligible.

I am happy with the status quo as they renewed my Porsche factory extended warranty for another year, which gives me piece of mind just in case this sub idle tremor is a precursor to my engine / drive line dropping dead. :P

Edited December 18, 2009 by bigbuzuki

[Reaction1]

My 2004 Cayenne S, with 75,000 mi on it also does this shudder. Has anybody successfully pinpointed the problem? What's the fix?

[SWFLHOMES]

I know this is an old topic but I've been trying to figure out this "sub idle" shake for 6 months. Call me crazy but I just replaced the front rotors and now NO sub idle shaking? Just coincidence or luck? Could the ABS sensor be tied into this or am I just reaching here?

[ARModen]

I know this is an old topic but I've been trying to figure out this "sub idle" shake for 6 months. Call me crazy but I just replaced the front rotors and now NO sub idle shaking? Just coincidence or luck? Could the ABS sensor be tied into this or am I just reaching here?

Was the shake related to rpm before? A warped rotor shake would be independent of the engire RPM (more or less). If it comes back, what you could try would be to coast along and put the transmission in neutral. Once the engine is smoothly idling apply the brakes, any shaking at that point would be brake related not engine related. If you don't see the shaking then, and you didn't get a shake when the transmission was shifted to idle, but you still get the shake under normal stopping conditions it is probably the transmission.

I think the tech in the earlier post was right on about it being a transmission thing for a lot of the low idle hesitation/shake problems. I noticed my boxster doing a similar thing as it got close to 100K miles. Since the transmission seals were leaking a little bit I had the fluid changed and the seals replaced. It shifts and goes to idle much smoother/faster now.

Edited March 10, 2010 by ARModen

[spyrwebs]

My 04 Cayenne turbo does the same thing but the RPM does not fall so low that it shudders. I only noticed it when I look at the RPM gauge. The RPM drops below to a certain point but I doubt its normal to feel the car shudder.

Also, from experience, I had another turbocharged car that shuddered when I came to a stop that it felt like the engine was gonna die. It turned out to be a leaking blow off valve. It could have different names such as air return valve, intake release valve, etc. But check that, its kinda hard to get too. Its located right above the Intercoolers in the wheel well covers, one on each side.

Edited March 10, 2010 by spyrwebs

[Reaction1]

I was able to isolate the problem. It will not do it with the A/C completely off. It is probably caused by some sort of electrical load. If idling and you turn A/C on, it will shudder, also. That's what made me try it without running the A/C. It is definitely something that wears out, because they only begin to do it after 50K miles or so. Maybe compressor clutch or electric fan motor gone bad. I have Duarmetric software and get no faults. Any ideas guys?

[RFM]

Cayenne AC compressors have no clutch, they are running continuously, the needed gas flow become arranged inside the pump. The advantage is that there is no tactile power drop, the disadvantage is that in case of a leak, the pump continues running without lubrication, they can not be switched off, not by the system and not manually. It is for this reason recommended to repair a leak ASAP, and the AC does not turn off for whatever reason. The pump will start seizing overtime.

[Reaction1]

Thanks, RFM, Now we can rule out A/C as the possible culprit. I also disconnected the fuse to the fan motor and determined that it did not prevent the symptom, either. I wonder if perhaps a faulty solenoid switch or electronic valve in the transmission, which only activates during the last and slowest downshift , just prior to the Cayenne coming to a complete stop, might be the cause. It is definitely some sort of load applied, that in turn causes the RPMs to dip momentarily, causing a shudder to be felt. Any ideas from automatic transmission guys?

Cayenne AC compressors have no clutch, they are running continuously, the needed gas flow become arranged inside the pump. The advantage is that there is no tactile power drop, the disadvantage is that in case of a leak, the pump continues running without lubrication, they can not be switched off, not by the system and not manually. It is for this reason recommended to repair a leak ASAP, and the AC does not turn off for whatever reason. The pump will start seizing overtime.

[SWFLHOMES]

Reaction1,

I isolated my low speed shudder to the A/C as well. RFM, it is when you put it on enonomy mode that the shudder dissappears. I have had my A/C serviced but it is definately a load issue that is tied into the idle. Any thoughts?

[wvicary]

So nobody wants to try cleaning the throttle body to see if that helps the problem??

[Reaction1]

I've cleaned the throttle body, which was fairly clean already. I had to use the Durametric software to reset it because it ran really rough after the cleaning. I still say that some sort of load is bringing the idle to dip just a bit below normal, and hence, the shudder.

[RFM]

It is obvious that a clutchless compressor, with internal flow control, consume HP when the AC is engaged. The difference with a clutch compressor is a smoother and more permanent power demand, there is no clutch which takes brutal HP when engaged, and releasing them back when they come disabled depending the in car (AC) temp. or the required engine power (full throttle). It is normal that when the ECONOMY button is pressed, the compressor flow control valves close to the minimum gas flow position, the compressor takes than about 1 HP instead of 5 HP in full flow position. Probably the DME react not well in some conditions.