05 Cayenne S transmission - almost stalling engine when halting

[Mongoman]

I need help - having spent over $5k so far trying to address this issue with my transmission.

It's a late 05 Cayenne S - everything at higher speeds seems fine - no problems with acceleration, no problems with hard up/downshifts - all my trouble happens when coming to a stop or accelerating slowly from a standstill. Here's the symptoms:

1) When I come to any stop, on the very last few feet, the engine seems 'locked' to the tranny so that RPM drops below idle, stumbles there for a second, and then returns to idle.

2) One time when the engine was cold, the engine even stalled when I came to a stop. Has not happened to me since, but it always drops below idle on a stop.

3) When I get going uphill, and then take my foot of the accelerator, the engine shudders as if the tranny was jerking. This only happens when very slow. I think it's not the engine as it idles perfectly smooth in neutral.

4) At very slow speeds, there is a distinct clunk whenever i go from acceleration to deceleration. It feels as if there was some sort of play between the transmission and the engine. Again, I only notice this at crawling speeds.

So what have we attempted to date?

- No error codes.

- Because of the rough idle, we changed all plugs, coils, and changed the oil.

- We even dropped the transmission and changed the torque converter seal.

All to no avail - I'm still having the exact same symptoms. It is really annoying because you drive around worrying that your engine may stall at any stop, and city traffic becomes a nightmare with every step off the gas and the faint clunk from the transmission.

After having sunk $5k into this already ($1k for a complete engine overhaul with plugs, coils, CP sensor; $2K to drop the tranny and replace the torque converter seal; another $2k to have the coolant pipes and engine mounts replaced) - this becomes really really unfunny. I don't even want to sell this thing knowing that something is wrong.

At this point, I wish I had already just paid $10k for a new tranny and be done with it; if I did it now, it would be the $5k i have spent already plus the $10k - wayyyy to hefty for a seven-year old car.

Any educated guess at what I could be looking at?

Thanks!!

[bigbuzuki]

Fuel pumps.

http://www.renntech.org/forums/topic/43200-rpm-dip-at-idle-on-05-cs/?p=231385

[Mongoman]

I had actually seen this fuel pump post before - I just didn't act on this suspicion because it wouldn't explain the clunk and the play that I seem to be having any time i go from accelerate to coast - it seems like the transmission has wiggle room. Something is not right, and changing both fuel pumps to the tune of yet another $2k is something that just scares me. Is there anything transmission-related that might be causing my symptoms? Or would you just give it a shot and replace the fuel pumps?

[working4it]

The fuel pumps are a DYI project and you can find them for less than $300 a piece...

[Mongoman]

OK, So let's give this a try then... I would be really excited to finally be able to put an end to these rumbling, stumbling and dipping issues. It feel's like I'm driving a friggin' 74 chevy.

[bigbuzuki]

The clunking may be caused by worn bushings on your suspension.

How does the rubber look on your front and rear control arms?

Also, did the transmission rubber mount and the upper engine torque arm get replaced together with the engine mounts?

Edited February 28, 2013 by bigbuzuki

[working4it]

Big has got a good point, I had clunking when stopping hard or on certain turns. Took a look and you can definitely see them cracked/torn.

[Mongoman]

About the torque arm mounts and transmission rubber mounts: I honestly have no idea; I can go check on it. If this was indeed done, it was hidden somewhere deep within the overpriced bills that I already had to gulp....

I'll check and get back. I would love this car to just ride smoothly again; it's just sad to see a car in perfect condition, with some issues that you just can't seem to be able to fix. If I have learned anything on these boards, it's that when you think you need a new engine or transmission, chances are it's an easy DIY fix - if you know what you're doing!!

Especially about these mount issues: Listening closely, the clunk actually is located more towards the engine rather than the transmission. Also, just for torque arm's sake, I revved the engine hard from idle in neutral - and - there it was - the distinct, dreaded clunk! So whoever brought up torque arm mounts first might really have a point. I'll keep you posted. Thanks for all the replies!

Edited February 28, 2013 by Mongoman

[bigbuzuki]

Regarding the torque arm, you should be able to inspect the rubber on the engine side.

The fender side of the arm can be inspected once you remove the trim on the fender.

Part number for the torque arm if required is 955 375 101 13.

Sonnen has them for $121.

[mwiadro]

Had some recent idle issues. Changing coils remedied all...except, a stumble at low speeds accelerating from a stop when pointed up hill. (I do also get a very occasional hard downshift coming to a stop.) Sort of your symptoms, too? I suspected it is related to tranny valve body - another common issue with these trucks. (expensive part, but DIY job.) Never suspected uphill stumble could be fuel pump. Will continue to follow your stumble/progress...

+1 on the clunks due to motor mount(s).

[Mongoman]

Well I guess all the above may hold true - and I may have a combination of issues going on here:

1) the idle dip - probably fuel pumps

2) the stumbling when I ease my foot off the pedal at very slow speeds uphill - probably valve body (or also fuel pumps)?

3) the clunking or play in the tranny - probably something engine mount- or torque-arm related.

There is one last thing that I can't put my finger on. Again, this only happens when slowly inching forward from a standstill uphill,

and only when you just inch forward without even gaining speed. Thats when it feels like the transmission does not slip smoothly and evenly - as any automatic transmission would - but i can feel jerking (or jolts) of thrust, much as you would get with a slipping clutch in a manual - could that also be the valve body? Really, I have never seen this behavior in any automatic transmission. For a while, I was thinking that this could also be related to the engine RPM problems, but when this happens, RPM remains exactly the same. The jolts do not seem to be coming from the engine... Everything seems perfectly fine on even terrain or anywhere faster than 1500 RPM, though

[mwiadro]

When I purchased my 04' S, it had a mismatched set of tires. All were bridgestones, but front pair were different tread pattern than front. Caused major PSM activity and what sounded like a driveline 'clunk' when stopping or taking off. After ruling out suspension/computer issues, immediately replaced all four tires with identical (Hankook Ventus) and the issues disappeared. Not sure if applicable in your case...

[Mongoman]

I have all four tires the same size - and, wouldnt PSM activity cause some light to illuminate? No illumination going on here. But a fresh thought.

[Mongoman]

OK, before I get started on this on the coming weekend, I'd like to share...

This is what Porsche claims: Did you know that over 70% of all Porsche vehicles ever built are still on the road?

They want to drive home a point for durability. If you look through the scheduled maintenance, there are items that are due every (!) 140.000 miles or

every 12 years.

So, here I am, with my hardly 7 year old Cayenne - not even having hit the 140k mile mark - and I refuse to succumb to the notion that I should have to live with certain issues because I'm driving an old car. Heck, there are 80's Carreras out there that are still driven on a daily basis!

Plus, my Cayenne has the perfect suspension - no clunks, no fade, no play; the perfect chassis - no dents, dings, nothing; a like new interior - so why should I have to put up with drivetrain issues? Clearly, those Cayennes were built to last and I want to have it perform flawlessly.

Aside from the idle dip issue, I have tried to replicate my engine / transmission shudder that occurs when I start uphill from a standstill, and then simply take my foot off the pedal - as the RPM spools down, I get either misfires (no codes though), or the transmission seems to jolt on the engine RPM.

I did this 3 times in this video - and you can see the stumbling with each of the attempts:

LINK TO VIDEO

I'll post updates as I go...

[jagman1]

I have a slight idle dip when slowing to a stop. It happens at about 3-5 mph. RPM's drop to about 400-500 (roughly 100rpm less than idle) for a split second. It feels to me like the transmission is a little slow at deselecting the gear (I'm assuming 2nd). I believe the car stays in gear for a second longer than it should, and that 'lugs' the engine for a second. With all the talk of valve body issues it follows the path of a common failure item. My issue does not sound nearly as obtrusive as yours, as in, nobody but me can notice this. Mine's been doing it since 55K miles and I'm at 93K now.

Just watched your video...

It doesn't look like the same issue.

Edited March 2, 2013 by jagman1

[wvicary]

Clean the throttle bodies and reset the adaption values. I don't think you have a tranny problem. Why would you think the torque convertor seal was causing this issue?

[Mongoman]

We did clean the throttle body; didn't change anything.

We didn't think that the torque converter seal would be causing my issues; but along the way, we found that it was leaking. We simply changed the torque converter seal because it was leaking ATF fluid.

I still don't know whether it's the engine or the transmission causing the stumbling as RPM spools down. The reason I'm thinking more tranny than engine is that this stumbling doesn't happen on braking. It mainly happens uphill. I think to the engine, it should make no difference is load results from driving uphill or applying the brakes.

[azelaya]

Hi there

I have similar problems in my Cayenne turbo, and i change the this 2 hoses and the pipe that appear on the following picture and the problem was solve, the hoses and pipe have cracks.

Maybe you have to check your if they are ok.

Sorry for my english

Tito

[azelaya]

Sorry

Here is the picture

I buy the parts from greg on sonnen porsche, great help.

[wvicary]

Although you cleaned the throttle body did you reset it's adaption?

[Mongoman]

OK, A little update on my issues: Changed both fuel pumps - IDLE DIP ISSUE GONE!!! :-)) All the other issues, most remarkably the stumbling as RPM spools down - are still there :-(

Azelaya, good thought on the vacuum leaks - even though someone apparently checked for leaks, it sounds like it would make sense to change the tubes - what symptoms were you having before you changed your tubes? The stumbling or the idle dip?

The trottle body would have been my first guess, so we cleaned that early on and reset the adaption twice. There are still no error codes. Before I get one of those new valve bodies, I guess my next step would be to change these vacuum hoses and pipes.

It is really frustrating to STILL have not been able to have figured out whether the stumbling is caused by the tranny or some engine problem...

[mwiadro]

always thought the fuel pump either worked - and produced proper pressure - or didn't. is there a fuel filter, too, that got changed?

(in my benz wagon, the fuel filter is integrated into the fuel pump - an expensive design. despite the service book calling for changing fuel filter/pump @ 90K miles, a couple beers with an MB tech and they all say, 'wait till it fails before changing!')

what scanner/software does your mechanic use?

[Mongoman]

Sad, sad update.

I'm sitting here with a new invoice on my desk - $1407 to have all 8 coils replaced by my local Porsche dealer. I could've changed them myself for less than $400, but I figured if they finally found the issue - let them have the business. Remember, by now I'm almost $7k into fixing a simple idle stumble issue!!! WTF???

As I went to pick up the P!G today, even as the car was handed over to me, it was still idling rough!!! How phucking arrogant is that? Charging me $1400 and then handing me over the defective car, probably hoping I won't notice?

I'm done with this. I left the P!G at the dealer and told them I won't pick it up until it's fixed for good.

Where the phuck are we? If I operated like that on patients, I would get my *** handed to me on a platter. I am beyond annoyed, and I'm starting to believe that no one can fix my idle stumbling issue. And yes - if it's not fixed by the end of the month, I'll post the name of the dealership also.

I'm soooooo over with this.

[wvicary]

Wasn't there a recall issued for the ignition coils on the V8's?

[Mongoman]

OK, here's the rundown: The idle RPM stumble issue still isn't fixed - bad as ever.

The explanation that we have come up with: Engine is fine. Transmission is fine. Driveshaft is semi-fine. But: The combination of engine mounts AND drive shaft may cause my issues.

When I take my foot off the gas, the engine goes from load mode into follow mode - causing the engine to 'wiggle' a little in the engine mounts. That wiggle then translates onto the driveshaft, which, in turn, also wiggles a little. By the time both wiggling has caught up with the new load circumstances, it comes as a jolt on the idling engine, which causes the engine to spool up slightly to account for the perceived drop in RPM - sending another jolt through the accumulating wiggle rooms. That way, this stumbling can travel back and forth along the engine mounts and drive shaft several times before it stabilizes.

This is frustrating, because to fix this would cost thousands. Anyways, I have learnt my lesson. Porsche's are one-way cars. Drive it for three years - then toss 'em. Or, if you plan on keeping your Porsche: Make it a decorative objective in the living room, and de-dust it every once in a while. That's about it.

I have had Mercedes, BMW, even Audi's with VERY high mileage - and never had any issue that would not have been fixed within a thousand dollars or two. But tens of thousands for a simple clunk? Thank you.