charlesj

Help! I have a 2005 Carrera S, and for the past year I have encountered and on and off reoccurring problem with misfire codes that I can't seem to track down. Addressing the obvious first, I have since changed all plugs and coils with factory replacements with no improvement

After resetting the codes, it can go for a day to several weeks before throwing again, and it ONLY triggers the check light while in the first minute of being on. If the car gets past the warm up phase, it does not throw the codes. Additionally, it seems a tiny bit choppy at first start, but the second you start driving or it warms of, the car runs perfectly and silky smooth. Currently, the car is throwing 301,303,304 and 305, though at times it has thrown other variations.

I did a bit of searching and found several people complaining of similar issues, but no clear answer that applied to my case/worked. Any ideas would be greatly appreciated.

iammulva

Sorry - I had the same problem (one time). The mechanic I took it to basically just switched the oil to 0w-30 and I picked the car up. Changed it back to 0w-40 within the week. That was 1-2 months ago. Problem has not returned. I still wonder what the cause was, but there are no codes now. Several people have posted potential causes. Let us know what you find out.

Spiffyjiff

clean your MAF. ive seen it do some funky (and intermittent) things. if that doesnt cure it, at the very least you'll have a clean MAF/you can rule it out cheap and quick.

Macster

Well, a WAG is that it is related to the VarioCam Plus system. The system has to switch to the low valve lift position upon cold start. With my Turbo I can I think know when this happens as shortly -- just a moment or two -- after a cold start the engine makes a bit of a cut out -- just noticeable -- and there is a corresponding dip in the oil pressure that does not seem to be proportional with the cut out.

Here is a video of what I'm talking about:

View My Video

Just after half way through, just a moment or two after I start the engine, you will see the oil pressure gage needle dip and the tach needle dip.

I mention this so that if you have an oil pressure gage you can watch the oil pressure when you start the engine and note how the gage behaves, how the engine sounds when this switchover takes place to see if it behaves the same way every time.

If (a big if admittedly) I'm right the SOP is -- if the car is under warranty -- to replace the variable lift lifters on the affected bank. In your case since the misfires occur on both banks both banks would have their intake lifters replaced.

Should add there is a set of diagnostic tests that would be done -- at least this is the case with my Turbo and I believe something similar applies to other engines with these variable lift lifters -- to confirm the lifters (or the switching mechanism) is at fault.

I do not recall the test steps.

BTW, the switchover and switch back is controlled by an oil fed through an oil line that supplies high pressure oil to the small hardened still pins -- one in each lifter -- that frees the high lift portion of the lifter to freely slide as the high lift cam lobe touches it so just the inner low lift cam lobe works the lifter. To restore high lift the pressure is removed and the pins should return (they have a spring) and lock the inner and outer lifter portion together so the high lift cam lobe works the lifter. Why this matters I cover below.

Anyhow, the tests are done and if the lifters are confirmed at fault then they are replaced. The thinking is they are bad because they are contaminated or defective.

Now I know I'm going to regret saying this but as iammulva posted using 5w-30 oil in his engine this is probably in some cases a reasonable shade tree mechanic "fix". While I would hate to even suggest you run 5w-30 oil this is a possible "fix". Maybe. At least it is something to consider.

But if you are going over to the dark side regarding oil why not stay on the good side for a while longer and consider these points? How is the oil in the engine? Is it kept reasonably fresh? Is is an approved oil? Mobil 1 0w-40 or a 5w-40 or even a 5w-50 oil? (My Turbo engine, VarioCam Plus and all, works just fine with Mobil 1 5w-50 in its oil tank but it worked just fine with 0w-40 too.)

Because of how the switchover works, it is an oil pressure triggered action, before I would run <sigh> 5w-30 oil I would be inclined to change the oil and filter replacing it with what oil I regularly use, an approved oil, (and in your car's case I hope you are using an approved oil) in the engine, then run the engine some long enough to get it fully up to temperature and run it in such a way the VarioCam Plus feature is exercised some, then change the oil/filter again.

What I would be hoping is this series of oil/filter changes with running the engine between them would act as a engine oil system flush, which is what I believe the 5w-30 oil does.

Now we could consider other possible causes of this cold start misfire. You have already had the plugs and coils changed which eliminates those items.

Since the misfires occur on both banks and do not appear to be consistently associated with a subset of cylinders, this suggests a common failure mode, common to both banks and all cylinders of both banks. One common failure point is as I have covered above the VarioCam Plus system.

Another is the MAF. While I really do not believe the MAF needs to be cleaned if you wanted to clean it -- while following all precautions about doing so -- I would not object. I do not think it will help but it only costs you time. Clean the thing over clean white paper towels.

If the MAF proves to be dirty you need to figure out where this is coming from and this could be from a compromised intake air filtration system. As long as the leak is ahead of the MAF it is not a leak that would affect the fueling like a post MAF leak would but it could allow unfiltered air into the intake and this could possibly foul the MAF. While the MAF has considerable margin to remain unaffected from anything that makes it through a filter it doesn't take well to being exposed to unfiltered or even partially unfiltered intake air.

You can also just disconnect the MAF at the wiring harness and ideally clear the codes even if there are none to reset all the learned fuel trims are reset to their factory defaults. Then with the MAF disconnected and other conditions as they were at other times the misfires appeared start the engine and see if the misfires return.

Kind of a long post, but I would add one more thing to try. It is long shot but you might just do an E-Gas calibration. If this thing has gone out of calibration it might not react as it should upon engine start and this could account for the misfires.

Long shot, to be sure. But you can do the calibration easy enough even easier than you can disconnect or clean the MAF. Oh, the owners manual should have the steps on how to do this calibration thing.

charlesj

Thank you immensely for the long reply. I have seen the recs about cleaning the MAF and have not gone there yet as the problem only seems to related to the warm up cycle, and it looks physically clean. Definitely something I can try, but was looking for more likely solutions

For the oil, I change it regularly with mobile 1, factory recommended weights (cant remember off the top of my head which that was). Problem has come into play at all random times.

Interesting write up on the VarioRam Plus issue - definitely not one I have heard of. Will look into that. Whatever the problem is, it is definitely occurring while the idle is a little higher on warm up phase. As soon as its past this phase and the idle drops, never has the issue.

Spoddle

I'm in the same boat and have replaced pretty much everything except the lifters themselves. Macster any idea how much lifter replacement on both banks should cost at an indy shop?

Macster

Sorry but I have no idea what a lifter replacement job would cost.

Well, let me modify this to say while I have no idea of what exactly a lifter replacement job wold cost, but I can offer some info that might be of some value.

The lifters can run around $100/each and there are 6 (intake) lifters per bank.

The amount of labor I would roughly estimate would be 6 hours per bank. The exhaust has to come off. The camshaft cover removed. The cams removed. The liters remove and replaced. The cams reinstalled and timed. The camshaft cover put back on and in doing so being sure it is absolutely/positively done right, then the exhaust goes back on.

6 * 2 = 12 hours. My dealer charges $150/hour. I do not know what indies charge. Labor then is $1800. Parts (just the lifters) is another $1200. Thus you are looking at a $3K bill. This does not include other parts and supplies.

For instance I recall from when I had the VarioCam solenoid/actuator replaced in my Boxster the camshaft cover bolts were not suppose dot be reused, so were replaced with new bolts. There is a charge for the sealant used to seal the cover to the head. There are other fasteners/hardware (at the exhaust) that often require replacement.

There is tax, too.

So, $3K is a very rough/ballpark estimate.

I am not sure I'd want to entrust this to an indy, though. If I did it would have be one highly recommended by others who have had similar work done. And I would want to be sure the same tech or techs that did this work before and upon which the rep was based were still there. A shop gets a good rep but the rep is really the tech or techs that did the work. They move on and the rep moves on with the techs but the shop's rep lingers on. It takes bad jobs to update the rep. You do not want your job to be one of the bad ones…

Perk10

OP - I had the SAME thing happen to me exactly a year or so ago. I replaced the plugs which looked ok, then the coils which looked fine and changed the oil/oil filter. I still got the same codes as you.

Then I changed the MAF to a brand new unit. About a week later the codes went away and I thought they were gone for good. After an entire YEAR later, they recently showed back up. Much like you, I only get the codes to pop up if the car is at a cold start. Like you said, if it doesn't happen at cold start, it wont happen. ALSO, my car runs silky smooth as well.

This has been driving me crazy so thanks for the post Macster. I'm going to try the calibration as outlined in your last paragraph.

Spoddle

Thanks for the rough estimate Macster. If I end up getting mine replaced I'll report back with the actual cost for the DC area.

Spoddle

I'm picking my car up from a local indy tomorrow who found and applied a recommended flash update. I'll report back if it ends up resolving my misfire issue.

Spoddle

Update... the misfire issue came back today. Back to the drawing board.

douvillier

Misfires that go away after warm-up generally point to a mechanical issue. Since its more than one cylinder, I would suspect a VVT issue. Oil change intervals are critical with VVT engines. I know what manufacturers state but start thinking about it at 3000 miles and have it done by 5000 or one year. Learn to change oil on your own, in the long run its faster and cheaper. Buy the oil filters in bulk and shop around for the proper oil for the best deal. That's my 2 cents and you know what that can buy you.

Macster

Bummer.

Based on what you've done with the plugs and coils, I am leaning towards the problem being with the VarioCam Plus system, probably the low/high valve lift circuit.

How much more investigation you want to do is up to you.

However, before I go on let me say that I have encountered at least one engine (a Boxster engine) that had multiple misfires and the problem was traced to a bad MAF.

So if you are feeling frisky carefully disconnect the MAF at the engine wiring harness.

Using an OBD2 code reader clear the error codes, even if none are present. Among other things this sets all the adaptation values/learned values back to their defaults.

Then start the engine and just drive the car normally.

Caution: If at any time the engine begins to run poorly, make any noises, act up in any way shut off the engine ASAP. Do not attempt to restart the engine. Get the car flat bedded to a qualified/experienced tech for a professional's diagnosis.

If the misfires are still present then the MAF is not the cause of them. Focus switches back to the VarioCam Plus system.

If the misfires are not present, then reconnect the MAF, clear the error codes again to reset everything, and drive the car again as you did before.

What you want is the misfires to return. If they do this is pretty conclusive -- for shade tree diagnosing -- the MAF is bad.

If the VarioCam Plus system comes back into suspicion, there are tests that can be done to confirm this is at a fault or the problem lies elsewhere.

The tests are pretty involved and can require two techs, one to drive the car the other to monitor engine telemetry during the drive.

There is too much to type in. I have this in PDF format from my 996 Turbo's factory manual.

While it is specifically for the Turbo engine the VarioCam Plus system is simlar in your engine and the tests if not the same at least give you an idea of what's involved. You might find this useful/of interest.

If you want send me a PM with your email address that can accept a 639KB PDF file and I'll respond with an email with this PDF file attached.

Spoddle

Thanks for your feedback Macster. I've read many of your posts and appreciate the detail you've provided.

Up until this point I've already replaced the following components.

- AOS
- New Bosch Spark Plugs (May switch to NGK) & Coilpacks
- Crank position sensor
- Cam position sensors
- MAF
- VarioCam Conponents (Actuator Valve & Actuator Camshaft on both sides)
- Reflashed ECU to recommended release

Here's what's left on my list, that may be contributing to this issue.

- Slow crank (replace starter cable, starter, and battery)
- AOS Leaking (replace tube that is leaking at connection)
- Replace coolant temp sensor (currently running low temp thermostat & recently flushed)

I'm curious to read the PDF you mentioned, and appreciate your input.

Macster

Well, you've done a lot.

Be sure you use the right plugs. I know everyone gets tired of reading this but to me the only plugs to use are the ones that the guy in the Porsche dealer parts department shoves over the counter.

While I do not necessarily think the plugs are the cause of the misfires, I know of one case (Cayman) where the owner installed some other plugs other than "factory". Now in his defense the plug cross reference chart listed this plug as the right plug for the application.

But the engine didn't run right. And he tried other things. Nothing worked. He posted a pic of the new plugs and the tip was recessed! Either the plug cross reference chart had a mistake of the plug maker was being quite optimistic regarding compatibility. He went back to factory plugs and that was it.

Since have replaced so much I'd hate to have this turn into just a plug selection problem, because what is left can be more expensive that a set of proper plugs.

Ok, with that out of the way do the starter cable, and battery. Be sure the alternator is putting out sufficient juice. This is important. If the alternator isn't working 100% the car's electrical needs may not be fully met. The coils can be the components to suffer as the voltage is too low to the coil and when the power is cut to the coil and the collapsing magnetic field doesn't generate a strong enough spark you can have misfires.

Don't get fooled by big voltage numbers for modern coils. While it is true modern ignition systems, and their coils, can generate 10's of thousands (in some cases 100,000) of volts of spark at low engine speeds the voltage may be a lot less, magnitudes less, possibly on the order of just a few thousand volts. Thus a drop off in voltage by a weak performing alternator can play havoc with the engine's ignition system and the spark it is required to generate.

You need to eliminate easy to address possible causes.

What is left is the possibility the engine's VarioCam Plus system, particularly the low/high lift hydraulic circuit is faulty.

This can't be fixed by replacing a solenoid. The problem lies inside the engine.

However, it is sometimes (often times) a problem with the lifters. They can get dirty or contaminated and this interferes with the rather delicate hardware used to control at the lifter whether high lift or low lift is active.

The fix is to replace all of the intake lifters on the bank with any misfires. If both banks have misfiring cylinders then of course the intake lifters on both banks get replaced.

The PDF I sent you and which you should have by now covers this some.