Pelican Parts Forums - Cayenne Turbo Misfire

My very recently acquired 2006 Turbo S 73,000 miles started misfire yesterday shortly after filling the tank with petrol.
The more I drove the worse it got until the point where it cut out completely and the engine check light came on.
I restarted and limped home

I have a Maxidiag EU 702 fault reader which supports a number of car manufacturers but not Porsche.
However the generic OBDII mode and the VW specific mode read the following errors:

P0492 Secondary Air Injection System Insufficient Flow Bank 2
P2177 System Too Lean Off Idle Bank 1
P2179 System Too Lean Off Idle Bank 2
P0300 Random Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0306 Cylinder 6 Misfire Detected
P0305 Cylinder 5 Misfire Detected

It felt like coil packs and was due a new set of plugs so I changed them all today.

Whilst doing so I noticed that the hose to the secondary air pump on bank 2 was completely disconnected, possibly explaining the first 3 errors

I couldn't see any cracks on the coil packs and their part number ended in 07 which from what I have researched means they were manufactured in 2009 ish, around the time of the last plug change

The plugs were all a similar very dark colour.

I cleared the errors and the check engine light now stays off.

Is there anything that could cause a misfire on all 4 of the front cylinders only?

I have visually inspected all the vacuum hoses.

Drove it again and it definitely still isn't 100% right. I got an occasional minor stutter both cold and hot.

Fault reader now only had the following:

P2177 System Too Lean Off Idle Bank 1
P2179 System Too Lean Off Idle Bank 2

I cleared them and it still misfired, but I only drove a short way and the codes didn't return.

I looked back through the limited service history I have for the car and in April this year the car was taken for a diagnostic test. The hand written report has the following:

1) Secondary Air System Bank 2 Below Limit Value
2) Vehicle Electrical System Voltage Via Main Relay. No Signal

It doesn't give the P numbers.

I'm assuming the first error was due to the secondary air pump hose being disconnected, could this have been off since the last plug change in 2010?

The second error is a little less clear from a quick look on the forums. One post suggests it is to do with parking assist, another to do with a faulty relay for the fuel pumps and another for a low battery voltage.

After reading the forums I found a few suggestions that low battery voltage could cause strange misfire issues so I attached a trickle charger overnight which showed the battery charge was less than 80% charged. My car has done very few miles in the last year and since I've had it I've been doing various bits and pieces which would drain the battery (tailgate shocks, tracing a Bose amp fault) and only done short journeys.

I also read about the PCV/Oil air separation membrane and have checked mine. It has a 1/4 inch split and a smaller pin hole. I have temporarily put a dab of glue and some tape on these. A new one is on order.

The engine now has a lovely creamy feel to it 99% of the time, smoother than any of the other Cayennes I test drove whilst looking.

There were no fault codes logged but I'm am still getting a very occasional stutter.

After getting the battery 100% charged I then tested the battery and it was indeed failing, so I fitted a new one.

The new membrane arrived so I fitted that.

All was well for a week until I filled up, and then about 5 miles later it started to stutter occasionally about 3 times over a 5 mile journey.

The battery voltage is good (12.9v when the car is turned off and locked). No faults have been logged

Could having a full tank of fuel cause a problem?

Any other ideas?