As Macster says, the emissions warranty (8/80K) will cover the ECU IF (an unfortunate IF for me...) you are within that time/mileage window. My car is a very early build and even though I am well under the 80K, I am about 6 months beyond the 8 year limit, so if I need an ECU, I'm hoping that my extended warranty will cover it. I have contact them (it is a high $$$ exclusionary warranty) and it sounds as though this would be a covered expense, but they need to see solid diagnostics to confirm this...so I'm still up in the air.

 

Have you considered checking to make sure the engine is well grounded? if you get a bad ground cable you might get bad spark until the engine warms and the conductivity is slightly better. when the car is warm and running well it might be worth trying to shoot the engine with a spray of water on the bottom to see if the codes come up.

Do you have any aftermarket stuff on the engine? aftermarket intake? I'd switch back to stock and see if that fixes the problem.

Do you understand how the ECU thinks the plugs/coils are bad? the ECU calculated the amount of air going in via MAF sensor in the intake, fires the injectors to get a good air/fuel mix, then checks it's own math with the oxygen sensors. If it finds that there's a lot of unused oxygen in the exhaust stream it increases the fuel coming in the injectors slightly. if slightly doesn't work then it thinks the plugs aren't firing and burning the gas. I'm oversimplifying here but this is the basic theory.

So.. if you are quite confident the plugs are firing well, I'd look closely at fuel delivery (perhaps your fuel filter clogged or pump is trashed) and the engine is not dumping in as much fuel as the ECU thinks it is. Or perhaps the oxygen sensor(s) are bad and it's confusing the ECU. I can't remember if there is a crossover on the exhaust before the oxygen sensors. If each oxy sensor looks at only 3 cylinders and you're getting fail codes on all plugs, i think you can pretty safely look at fuel as your problem.

if you're looking at fuel, I think I'd just put a fuel gauge inline right at the injector rail and verify that you have good fuel pressure while the engine is choppy. If you have low pressure when choppy look at the fuel pump, filter and regulator. Actually this reminds me a lot of a bad fuel pressure regulator on another car I worked on one time.

The other possibility is of course mechanical failure of valves or something. I think this would probably have to be a failure with the variable valve mechanism since you're getting failures on all cylinders. I could see one bad hydraulic lifter if you had one bad cylinder but it's on all cylinders. If you had 6 or more bad lifters that would be a pretty incredible coincidence. I think I'd dig into any valve stuff only after I really chased the **** out of fuel delivery and sensors.

good luck.

 

ORRR... might be worth it to through a cam position sensor or crank position sensor in there. Usually those result in a no start condition when they fail though. So pretty unlikely.

One other diagnosis tool is to run the engine while choppy, then pull a few plugs and "read" them. Get the oldest tech in the shop to do this. are they sooty? are white? White would make me chase fuel delivery. Sooty would make me chase things like engine ground or checking to make sure the spark is strong.

 

Thanks for your input, 997_rich! I hope my tech reads this forum!

 

I think you'll probably have to print it and discuss with your tech. Given what you pay to have your tech work on this car it's part of his responsibility to take the time to explain his/her thinking with you. Sometimes the service writer gets involved if he's more articulate. These kind of "lemon" problems will go one forever unless you can get this kind of group thinking going on.

Or... you may find that you sell the car and someone makes an easy fix to get it back to life. I have a friend who did this over a period of years with many cars. He'd buy basketcases and fix them (always cars he knew well). He bought a non starting 911 for a song and fixed it 20 minutes by putting the rotor in properly (it was backwards). Your issue probably isn't that simple, but I guarantee it's fixable and I strongly suspect it isn't a $10k fix. You just need the right kind of logical problem solving person on the job.

 

To the OP how many miles are on your 997?

 

lifter issues are NOT uncommon with all the amount of 996/997's we deal with everyday:-(

 

Further thoughts on this...

All general hardware that can result in misfires has been replaced: coils, pugs, MAF, etc.

The problem only occurs when the engine is cold but then not all the time.

The problem never appears when the engine is not cold.

The misfires are in all cylinders, so the failure is a common failure to both banks.

One thing that comes to mind is the crankshaft position sensor. If this thing is intermittently faulty (or possibly loose or with a bad wiring connection) it could result in misreading flywheel speed/acceleration and and this would result in the DME reporting misfires where there are none. However, I have never heard of one these being intermittently bad. I have heard of a few cases in which one has been incorrectly installed or was disturbed during some other work and have caused problems.

If the engine rough running concurrent with misfires is accompanied by the engine spitting back/backfiring through the intake this suggests a lean condition.

Since you have replaced the MAF which is responsible for intake air temp this leaves the coolant temp sensor.

This is a question I'd want answered: What is the ambient air temp, the intake air temp, and the coolant temp when the engine misbehaves?

I would expect all to be close to each other.

Since the engine has its good days even from cold you can use the temp readings from those days to set a baseline and then look for some way out reading.

It is possible the coolant temp sensor is supplying a much warmer reading and the mixture is not as rich as it should be on a cold start and the engine misfires (and spits back/backfires through the intake) for a bit until the sensor supplies readings which are closer to the real temperature of the coolant and the engine.

One thing you can consider is buying an OBD2 code reader/data logger that also allows you to capture OBD2 data for later analysis.

Have this reader hooked up and recording and capture the data from a cold engine start to beyond the point the symptom goes away.

You want a data set from when the engine didn't misbehave.

Save this data.

Then every time you start the engine cold record until you record data from a bad engine cold start.

I think comparing the data will then tell you and a tech something.

If the data looks the same... this tells you something and that is the source of the problem is buried deeper than a sensor. I would then look at the DME though I have put this first it would be my second choice, and the VarioCam Plus system, which would be my first choice.

For some reason the VarioCam Plug system is not working right and the engine doesn't have the valve timing or lift it expects/requires at a cold start.

The timing is controlled by two separate actuators. Since the error codes are from both banks it would have to be something common to both actuators. I do not know the internals of these engines well enough to know if there is any common failure point. A tech should know, though.

How I kind of suspect the variable valve lift is controlled by one device/valve/switch that routes high pressure oil to oil passages that then feed this oil to the lifter bores and activate the locking pins that move and unlock the inner lifter from the outer lifter so the outer lift can move up and down without affecting the valve lift. The inner lifter is then moving the valve open from the low lift cam lobe.

Thus I would suspect this variable valve lift control mechanism.

Another area to suspect would be the fuel supply and pressure.

Does the behavior appear to appear more often or less often with a change in gas tank level?

Does the car have a serviceable fuel filter?

Last and this can be a real chore as the wiring harness is not easy to inspect -- mirror on a stick/swivel, bright light, steady hands helps -- has the engine harness wiring been inspected for signs some critter has been chewing on the thing?

While the tech may not be able to spot signs of gnawing he can/should look for signs rodents have been in the car and if he finds this then... I know in one case the engine had to be dropped to really get a good look at the harness which was found damaged and had to be replaced. The complaint the owner brought the car in for? CEL (I do not know the error codes though) and sick running engine.

You can consider the above, or run them by your tech. He may be able to dismiss some or all without having to go the trouble of performing any testing.

 

Man, I feel so bad for you. I had similar issues for a short spell, though plugs/coils solved my issue (knock on wood). These types of scenarios, while the exception, are simply terrifying. I wish you all the best and hope for a speedy (and permanent) repair so you can sleep at night.

 

kingian65 i had the exact - exact same thing happen to my 2005 997 C2.
Not sure if you have found the solution yet, but before you spend a lot of money, this is what finally worked for me: After replacing all the coils and spark plugs, light came on again. Only at start up, car ran rough for a few minutes, then fine. Then CEL. --- random misfires code on all cylinders.
I replaced the battery, and it went away for a while. Then it came back. Same CEL and code. Checked alternator and was only charging about 11-12 volts.
Replaced the alternator - now charging at 13 volts. I have never had the problem again. That was two years ago, and i use it as a daily driver most of the year (except winter).
The dealership had no idea why this was happening. I normally stick with genuine Porsche parts, but the alternator was $2600 + tax. I was not even sure this would fix the problem, so i bought an AC Delco alternator for $380 or so with lifetime warranty. I have put over 30,000 miles on the car since with no CEL.

 

The alternator could actually explain the behavior the OP reported.

Since I last posted I encountered a Cayenne (I can't recall now maybe it was a Panamera) in the service bay at the dealer. I spotted the diagnostics computer connected and this piqued my curiosity and I asked the tech what's up with the car?

He told me alternator. What the car would do is the engine would start and idle just fine. After a few minutes it would start to run rough, then get worse with CEL coming on and other warnings. Not too much later the engine would die.

The tech would turn off the key and let the car sit a while and it would do this all over again.

What was happening was the alternator was ok for a while, a short while but after just a few minutes (or less) of engine run time the alternator would not generate sufficient electrical power to satisfy the considerable electrical power needs of the engine and the car. As the alternator's output fall away the battery would of course be the only source of electrical power but its reserves simply couldn't keep up and the behavior I described above was the result.

 

How do you test the alternator?

I have a problem child CEL. it only comes on at start up, but it doesn't run rough. Fuel Ventilation Module. Replaced the pump, didn't work. A technician trouble shot it and couldn't find any cause. I've heard of batteries and other electrical gremlins causing this sort of thing, but I haven't tested the alternator. After I reset my CEL it stays off for about three days and comes back.

 

I don't recall. I've been fortunate that none of my cars have had an alternator problem.

I sort of recall it involves verifying the alternator puts out sufficient voltage and this would be over the 12 volts of the battery. Based on what my Turbo's volt gage reads I'd say as long as you measure the voltage at 13 volts or higher but not above 14 volts the alternator is ok. My Turbo's volt gage runs a bit over 13 volts but never over 14 volts. How much electrical load there is plays a role. The thing reads higher after engine start but after say 15 minutes the voltage drops some as the battery is topped up. Turning on the A/C or headlights can have the volts drop to near 13 volts.

The trouble is it might start out ok but its output falls off. As I mentioned in an earlier post in this one particular vehicle the alternator output would drop off shortly after engine start.

In some cases an alternator might work just fine for longer. Or the drop off in output could be intermittent.

If you want better info, here's a link with some info you might find useful:

http://www.wikihow.com/Check-an-Alternator

 

I've found this thread useful and, seeing as I have similar symptoms as the ones discussed above, thought that I'd contribute with my own experience.

I get the CEL when my 997 (2006 4S) is cold, car starts fine and goes to ~1200 rpm, then after a minute or two engine settles down to 800rpm idle and thats when the CEL comes on. I'll add that I don't regularly use my 997, at best every couple of weeks, sometimes even 6 weeks between uses and the most was just recently a couple of months. When I do use it it runs perfectly with full power and no strange or irregular noises/vibrations etc.

My CEL happened first time in Dec 2013 (bought the car in March 2012) I had it towed to the mechanic as at one point it was firing on only 5 cyls. They checked the coil packs and said all are good, cleared the faults and it didn'ty happen again for another 7 months, when it started happening again but a blip of the accelerator cleared it. Again, in this time I used the car on average once a month.

It then happened again couple of weeks ago in Dec 2014, this time twice in a row and next time I started to car (today, to take to the mech) it was on right from the start.

We connected the car to an Autologic and it was showing errors on one bank in cylinders 4, 5 and 6, something to do with the valve control. There were two sets of errors, can't remember exactly what they said. The mech (Matt, thanks again in case you're reading!) replaced the solenoid with a spare one he had and cleared the fault (the other idea was to swap with the other bank and see if the error then showed up on that bank).

So far all ok but I haven't gone through a cold start yet, lets see next time!