My 2005 Carrera (58K) suddenly showed a CEL shortly before annual emissions testing. Nearly all cylinders were reporting misfires. MFA, all plugs and coil packs were changed 18 months ago. Car runs fine. There's tappet noise at startup but it quiets down in first 2 minutes. My shop ran extensive diagnostics--vacuum leaks, etc.--and recommended dropping the engine to replace all the lifters and lifter racks. Seems pretty drastic and counter-intuitive. I can't drive this any further until the light is cleared and it gets a state emissions sticker. Anyone have any experience with this?

 

The short answer is yes. The longer answer is lifter noise that takes 2 minutes to quiet down suggests the lifters need to be replaced provided the oil pressure is good otherwise, and the oil is of the right viscosity, type and is not too low or too full and is reasonably fresh.

While I do not have the factory manual for the 2005 Carrera I have one for my 03 Turbo and while these are of course different engines both of these engines have VarioCam Plus (variable intake timing and low/high intake valve lift adjustment).

My Turbo factory manual has a section on diagnosing P0300.

Possible causes:

fault in ignition system
fault in injector system
flat-base tappets intake valve lift fault
mixture too rich
mixture too lean

Then comes: Valve lifter clattering.

This is caused by dirt in the lifter. When the Check Engine Light lights up a chattering valve lifter may also occur for a certain time. The DME control module registers sporadic misfiring at one or more cylinders. The mixture adaptation values are normal.

Remedy:
1) Remove lifter bores [sic], check for damage and blow out oil passages.
2) Replace all valve lifters.
3) During the test drive listen for lifter noise.


Camshaft control times adjusted.

The camshaft control times have changed. No chattering noises occur. The DME control module indicates misfiring for the entire cylinder bank 1 or 2. The mixture adaptation values in the upper and lower load rages are generally normal.

Remedy:
1) Carry out raw emissions measurement.
a) Reset mixture adaptation values (disconnect the battery). [sigh]
b) Disconnect oxygen sensors.
If the differences between bank 1 and bank 2 is greater than approx. 0.8%, then:
1) Set the camshaft control times again.
2) Read test vehicle.The mixture adaptation values must be normal.



VarioCam does not switch over completely

And so on.

I can't type all this in, but I have a PDF file that I can email you if you private email me with your email address that can accept a PDF 639K bytes in size.

While I took this from my Turbo factory manual I believe your Carrera would receive the same basic tests.

'course, my thinking too would be you would show up at the dealer with some knowledge of what tests could be done when the engine is misfiring like your's and then ask why these weren't done?

Now maybe the techs just know that the tests are going to end up with them having to replace the lifters and they are trying to save you some diagnostics labor costs. (Roughly one could be looking at 3 or more hours labor as some tests require two techs. One to drive the car and one to observe various readings with a portable diagnostics computer.)

I bet the techs have seen enough engines with this symptom to know what's going on. I mean Porsche didn't work out all the test steps because of a hypothetical problem. I'm sure this issue has come up since Porsche switched to hydraulic lifters and some kind of VarioCam system and the test steps were worked out using an actual engine with the behavior described.

 

First off, thanks to Macster for his great reply to myquery. The end result of the ensuingrepairs was to try an intermediate sort of fix; the shop replaced the twohydraulic solenoids that change the valve timing. They'd seen this fix work before and now theengine fires up smoothly (it had developed a lumpy, rough idle at startup) andthe valve clatter is greatly reduced. The car passed its emissions test. The shop noted that a lifter replacement in the future is still apossible outcome, but the number of tapping lifters is probably down to justone or two, and once the car runs for a few minutes the noise generally fadesinto the normal background. The shopdescribed the solenoids as being in the oil circuit and changing them andcleaning out the local gallery was possibly responsible for better oil flow tothe lifters as well as overcoming the misfires. I had for some time felt that there might be a problem with the valvetiming mechanisms as there was a pronounced bump-up in power (felt like an old-timecarb lean surge) at 3000 RPM that seemed out of place in this engine, as if theadjustment was hanging up and then banging in with an on-off feeling. Prettymuch gone now. So, a happy ending,albeit with a lot of hours of diagnosis to pay for.

 

Glad I was able to be of some help.

The bump up on power is probably not valve related. My info is valve timing adjustment occurs a very low RPMs (1400 RPMs at least in some models) and again at a bit over 5K RPMs.

Low lift only occurs at very low engine RPMs way below 3K RPMs. (It is a feature to reduce start up emissions.)

What happens at 3K, at least in some models, is the intake resonance flap opens and the engine receives a bit of a kick (and intake howl bump too) from this.

I'm still of the opinion that lifters that take a couple of minutes to quiet down is not a good sign. But what if anything to do about it will have to be between you and your tech. Maybe taking the wait and see attitude is the best course for now. The noise could be from dirt in the liters and with use this might get removed and filtered out.