Intermittent Cylinder 6 Misfire & Valve Lift Code After Extended Driving – Possible L

[cvalue13]

Hi all – I’m normally over in the 997.2 forums, but posting here in hopes of collecting thoughts from others who may share experience with Porsche’s VarioCam Plus and hydraulic lifter systems.

I’m troubleshooting a cylinder-specific misfire and valve lift issue on my 2010 997.2 Carrera S (MA1.01 engine), and for models sharing similar engine architecture (MA1 family, VarioCam Plus system, hydraulic lifters/valve lift solenoids), I’m hoping some of you might have encountered or solved a similar issue.

Full details below — thanks in advance for any input or shared experience.



Mine: 2010 997.2 Carrera S (manual, RWD, 45K mi, all maintenance up to date).

My tech suspects a possible mechanical lifter failure on Cyl 6. While certainly possible, the fact that this only occurs when hot, and not cold, seems counterintuitive for a classic lifter collapse.

Car ran smoothly beforehand (including prior owner, whom I know well) with no startup issues, no misfire at idle, no abnormal engine noises, smoke, oil burn, or noticeable soot difference between pipes..



The issue:
After about 1 hour of spirited driving in ~80°F weather, I experienced a sudden misfire and solid CEL. Codes were:

• P0306 (Cyl 6 Misfire)
  
• P1360 (Valve Lift Control – Cyl 6)
  
• P0455 (Evap System Leak – Large)

After parking for ~20 mins and key cycling, CEL remained but it ran smoothly for the ~1hr drive home at <3K RPM. Misfire returned once the engine was fully hot again near home.

This same pattern has now happened twice—always after 1+ hour of moderately hard driving.



Tech findings so far:

• Swapped valve lift solenoids/actuators bank-to-bank – issue stayed on Cyl 6.
  
• Cleaned valve lift filter screen (minor grit found).
  
• No other filter debris found.
  
• CEL didn’t return during ~70mi of test driving (but not at high temps/load).

Misfire does not occur on startup or under normal, cooler weather around-town driving. Also:

• No ticking or "tinking" sounds
  
• No oil consumption, smoke, or soot imbalance
  
• P0455 has returned with the same event each time but may be unrelated

My, my tech reasonably now suspects a possible mechanical lifter failure on Cyl 6. But we're puzzled that the failure is isolated to just one cylinder, is reproducible under heat/load (rather than startup/idle).



Looking for input on:

Other possible root causes (thermal oil pressure loss, wiring, lifter oil supply?)

Mechanical vs. oil pressure/control-related failure?

Further diagnostic suggestions before invasive action?

Jake Raby's video on bore scoring and lifter failures both gives me some comfort that it's prob not bore scoring, but where lifters are concerned the video also doesn't seem to address the above fact-pattern (instead discusses more common idle/cold, tinking, full bank, etc., type lifter issues).

However, he at one point in the thread says that sometimes these engine's lifters are sensitive to oil, and he's seen misfires when the car "needed" an oil change (I've just had one), or simply didn't like a particular oil. The latter suggestion seems vaguely possible given my issue arises when temps/rpms are up?

Thanks in advance for any ideas or experience. Little to nothing online with this fact-pattern, so hoping to not only dig up info but also create a record for others, pending diagnostics/outcome.

[JFP in PA]

As pointed out elsewhere, these engine's valve lift and cam timing controls are susceptible to ANY amount of debris or sludge build up in the oil system because both depend upon the engine oil to pass through very small orrifiaces to operate these systems correctly. One debris partical is enough to force the system to throw codes..........

[CogitoErgoZoom]

I agree that if you found debris you should focus on that first.

Question: have you changed the oil and filter? I would add some LiquiMoly Pro-Line to the current oil, let it idle for 10-15 minutes and then change the oil.

Also, have you checked the connectors for corrosion, bad solder joint, etc? Thermal expansion could be causing an intermittent open somewhere on the harness between the valve lift actuator and the ECU.