fmar

Hi fellow Porsche enthusiasts!

I just got my first Porsche last week, a Cayenne S -08. Almost had an entire week of happy ownership before I noticed some vibrations and (what I think is) engine misfiring.

Did a bunch of research online which often pointed to ignition coils and spark plugs. The car has done around 111k miles (or 180k km), so it makes sense for the coils to be replaced.

Started working on the car and sure enough two out of the eight ignitions coils had cracks in the plastic. Drove off and bought two replacement coils at a Porsche dealership, went back and installed them - hard to say but I do believe the engine runs slightly smoother. Although not as smooth as just last week, i.e. noticeable vibrations on idle and occasional misfiring causing the car to jerk when driving.

The remaining six coils looked fine, but after consulting my friend Google some more - I learned that the cracks on the coil housing may just be cosmetic and not affect function(?).

Would the logical next step be to replace the last six ignition coils or maybe try something else?

In the inspection book, spark plugs are noted as replaced earlier this year. So they should be in good shape, however as I bought from a smaller local dealership and the inspection book is in German, I'm not 100% convinced. Is there any easy way to verify that they indeed were replaced? Only 3k miles since the stamp in the book...

I might also add that I do have an OBD reader, did some quick checks after replacing the two coils. The engine seems to still be as uneven on idle, ranging from lows at 534rpm and highs at 625rpm. Didn't measure this before replacing the coils but I do believe it was quite similar judging by the vibrations and misfiring. During this entire troubleshooting, I haven't been receiving any fault codes or error messages.

Very thankful for all help and input I can get!

Kindest regards from Sweden

Rossi

I had some issues with rough idle recently on my 09 GTS. Ended up getting the check engine light. All sorted now, runs like a charm again.

Suggestion:
Clean the MAF sensors, throttle body and both air filters.
Check for leaks, like the throttle body seal and replace if necessary. $10 for the seal.
Fuel filter would be the next thing I would look at.

deilenberger

There is also the oddball problem of bad engine mounts - especially the torque arm at the top of the engine. Take a careful look at the bushings in it. If they're cracked the arm needs to be replaced.

fmar

Thanks for your input, I'll try to check your suggestions tomorrow. However, as I interpret your post, these things could be the reason for the rough idle but could it also cause misfiring?


I did actually notice that the notorious "Cayenne torque arm" had a small crack on the rubber bushings, so I'm looking to get it replaced quite soon. Do you really think a small crack (not cracked all around the bushing yet) could cause vibrations at idle? I'm certainly no mechanic, but one guess would be that the vibrations are caused by poor ignition in one (or several) or the cylinders. And also what I believe is the occasional misfirings

Rossi

Correct. Just something I addressed recently on my car.

fmar

So far I've managed to check the air filters (both looked brand new), cleaned the MAF sensors and also the thottle body. The throttle body wasn't super dirty, but there definitely was some oily residue there, now it looks brand new. Also the seal looked just fine.



I'll try to put it all together again (fingers crossed I'll manage) and go for a drive to see if this resolved the issue.

And if not I'm a bit skeptical that the fuel filter could be the culprit, bear in mind that we only have gas with an octane rating of 95 and higher. Shouldn't this mean that the fuel filter lasts a very long time?


Nearly done with cleaning the throttle body, just some residue left on the edges as shown on the pic

jbanuelos

Is there any precautions you took when cleaning the throttle body? Specifically with rotating the butterfly open to clean the edges of it? I'm also planning on cleaning mine soon, I have the seal replacement but just haven't gotten around to it yet. Thanks!

fmar

I tried to handle it with extreme care as I'm told a broken unit means a visit to your nearest Porsche auto shop to refit the engine with a new throttle body And reprogram the onboard computer to work with the new unit.

That being said, I gently tried to rotate the butterfly but it was quite stiff. However, moving it just a couple of mm made space to clean off the residue. It came off super easy, I used CRC Bräkleen (brake parts cleaner) that I was told should work just fine for the job. CRC also offer a "throttle body cleaner" specifically for this purpose, so I do recommend going with that one (unfortunately it was out of stock in all stores near me).


EDIT: If you look in the background of my pic above, you see all the oily residue that more or less just rinsed off with the CRC Bräkleen.

fmar

Everything is now put back together and I just took a quick test drive. Unfortunately, the issue is not resolved - yet.

I think I will replace the remaining 6 ignition coils, hopefully one of them will prove to be the culprit. However, that will have to wait until mid next week as I'm just about to go on a euro road trip. Goes without saying that the mighty Cayenne won't be able to join this time around, maybe next year.

deilenberger

A fuel filter is unlikely to restrict flow at idle speed if it can provide adequate flow at higher speeds. Since your problem is at idle - it's not the fuel filter. And changing it isn't trivial.

Replacing the rest of the coils is probably a good step - if one or two went bad, their buddies in adjoining cylinders are sitting there thinking about going bad too - if they haven't already. Since you're uncertain if the plugs were actually changed - it would make sense to change those while you're doing the coils.

ScootCherHienie

The octane rating of the fuel has nothing to do with how long the fuel filter remains "clean". The ONLY thing octane affects is the resistance of the fuel to auto-igniting at high pressures/temperatures that can happen at or near the bottom of the power stroke (causing engine "knock" or "ping"). Fuel with higher octane is slightly slower to burn during the power stroke and resists suddenly exploding at or near the bottom of the power stroke. There is no more power or energy or cleanliness in higher octane fuel compared to lower octane fuel. And regarding Octane numbers... Europe and the US calculate octane differently. European octane numbers are higher, but US fuels and Euro fuels are eequivalent when octane is calculated the same way for both fuels. There are even more ways to calculate the octane number than the standard "Euro" and "US" methods... fortunately consumers only have to deal with one means of calculating octane in their geographic area.

As for coils... if I'm not mistaken, the Cayenne should "know" when there is a misfire and report that as a code with Check Engine Light illuminated. Since you are not getting misfire codes, it could be possible your rough running is not related to the coils. That said, coil cracks can indicate a bad coil but not always. A cracked coil is likely to fail sooner rather than later so may as well replace any with cracks. And coils without cracks can be bad. Also, when the engine computer detects a misfire, it should report the cylinder number as well. If the engine is operating roughly, but there are no codes, the problem may not be a misfire even if it feels like there is a misfire. That leads back to other suggestions like the motor mounts but could also be something else in the drive train causing a shudder that could feel like a misfire.

fmar

Hi guys, just got back from my road trip yesterday and finally today I replaced the remaining 6 ignition coils... And problem solved! The engine runs much smoother with the occasional very slight vibration (I'm being really really sensitive right now). I would say the problem is about 95% fixed, as for the last 5 or so per cent, I suspect that replacing the spark plugs would be the fix needed.

To sum up, this is what I've done so far.
-Added injector cleaner to the tank (didn't have any noticeable effect)
-Replaced two ignition coils that had visible cracks (may have helped some but didn't cure the issue)
-Cleaned the MAF sensors and the throttle body (didn't notice any change)
-Replaced the final six ignition coils (and finally, this did the trick!)

I did consider typing up a guide of the procedure but I found some very helpful videos so instead, I'll link to them in case anyone else on the forum needs to get their coils and/or spark plugs replaced.
-Facelift: -Pre facelift:
All in all, this set me back quite a bit - around $500 or so. Especially considering the car is only worth about $13,000. But on the other hand Porsche wanted $300 just to troubleshoot the car, so not too bad after all.

Thanks to all of you that provided your valuable input and much-appreciated suggestions!

ScootCherHienie

Just a note about "fuel injector cleaner" -- They appeared in the early days of mechanical fuel injection, probably the 1970s and served a useful purpose THEN. But today these products are a scam and aren't likely to do ANYTHING... EVER. If you look at the label, the ingredient is alcohol. There is already 10% alcohol (at least) in gasoline these days. The alcohol that has been in gasoline for a long time now does the same things as the alcohol in "fuel injector cleaner". In addition to that, the federal government requires all gasoline to have additional fuel additives that keep fuel injectors clean in addition to the alcohol already in the fuel.

ScootCherHienie

As for the remaining roughness... I would suggest a fuel injector actuator is possibly not working reliably. Modern fuel injectors turn on and off with a solenoid-type actuator. Much like the spark plugs only fire at the optimum moment, fuel injectors only deliver fuel to the cylinder at the right time. If the actuator on the fuel injector begins to fail, you can experience missing. This sort of failure could be, but not necessarily be, heat related also--might be worse when cold or might be worse when hot depending on the type of failure. Could also be problematic at any temperature. There is also the issue of possible oxidation in an electrical connection going to a fuel injector. If there is an electrical connector in the path to each injector (I don't have wiring diagrams so not sure) and there is a pin/socket or blade-type connection in the connector, it could have oxidized over time. Unplugging and reconnecting the connector may solve the immediate issue. If that does the trick, you can get some Caig Labs DeoxiT Red in a small spray can (sells for $15 -$18 usually) and spray both halves of the electrical connector and you'll never have a problem with oxidation in that connector again. It fixed electrical problems in a 911 for me and they stayed fixed for 25 years of ownership.

deilenberger

Scoot - have to disagree with your blanket condemnation of FI cleaner. Chevron "Techron" is not alcohol based. It has some amount of Stoddards Solvent in it - and the proprietary cleaner Chevron invented called "Techron." It does work, and alcohol isn't going to work like it. Back in the days of some bad gasolines BMW worked with Chevron to try to solve a coking problem on the M30 series engines. The back of the intake valves would get so carboned up (coked..) the cars wouldn't idle and would barely run. The carbon would absorb gasoline during cold startup, then release it as the engine was running, causing the O2 sensor to trigger the ECU to cut back on the injection duty cycle.

Techron was the answer. BMW re-labeled it (I think they still do actually) and sold it as BMW Fuel Injection Cleaner.

The final answer was BMW's definition of "Top-Tier Gasoline" - which has to meet certain standards in order to use that title. Most modern brand name gasoline meets the standard. A google of Top-Tier will turn up the website, specifications, and what gasolines meet the specifications.

Even with Top-Tier gasolines - there is always a possibility that a misfiring coil resulted in a condition in one or more cylinders injectors are partly crudded up, and the spray pattern isn't ideal. In that case, adding a bottle of Techron might help. It certainly did help with non-direct injection systems, I'm not certain how much it will help with a direct-injection injector (since it sprays right into the cylinder), but it's not going to hurt.

And cleaning the injector contacts is a good thing to do - but not so simple with direct injection since they're located under the intake manifold.