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My purge valve would stick open when warm. Using a set of jumper leads, I tested the valve with a 12V battery starting from cold. It was initially closed, and then after a few cycles with the battery it would stick open. This intermittent failure may also contribute to the car running fine again after sitting overnight.

You could crimp the vacuum line prior to refilling, and that should eliminate your stumble (assuming its the PV that's leaking). But you will throw a CEL after a few minutes because the sensor that's looking for vacuum on the evap system won't find it thanks to your crimped hose.

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Octane 95/97/99 won't change anything adversely. Higher Octane will actually reduce knock, allow more ignition advance and increase power and torque with less risk of pre-ignition. So higher Octane eq

My 04 cayenne turbo had the same issues with intermittent stumbling and it ended up being the left fuel pump. I spent one Saturday replacing both fuel pumps plus the regulator and the filter all at th

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Despite not having starting problems after refuelling, as the cost of a new purge valve is considerably less than what I imagine the cost of vehicle recovery would be, perhaps that's the route to take.


What I can't fathom is why, without tampering with the evap system, you are not seeing a fault code related to that. Could it be that the reader that you have is not giving you the full picture, I wonder? 

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Although I still think an intermittently faulty PV is the most likely cause the other possible faulty component could be a saturated evap canister. 

To disprove the canister you could run the tank down to 1/4 then fill only to 3/4, this would in theory not saturate again the canister (unless completely clogged which one would expect a code for tank venting problems and difficulty in filling up, nozzle keeps clicking off as air in tank can't vent out quick enough). If the car ran fine after doing this a few times it may point away from the PV. 

100 bucks for the pv, I would have already done that! 

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The volt meter is showing 13.9 or 14 volts whilst driving 


My fault code reader doesn't support Porsches but the VW option appears to read all the codes. I have a PIWIS cable on order.


I have also ordered a purge valve.


If my purge valve is sticking open only when hot, if I simply unplug the cable to it before the cold start before my next fill up will this tell me anything?

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7 minutes ago, DannyHoffman said:

The volt meter is showing 13.9 or 14 volts whilst driving 


My fault code reader doesn't support Porsches but the VW option appears to read all the codes. I have a PIWIS cable on order.


I have also ordered a purge valve.


If my purge valve is sticking open only when hot, if I simply unplug the cable to it before the cold start before my next fill up will this tell me anything?

PIWIS cable? 


Fit the PV when it comes in, until then not much point scratching your head more. 

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4 hours ago, DannyHoffman said:

PIWIS Porsche Integrated Workship Information System


I'm thinking of what other possible tests to do incase I have to fill up before the purge valve arrives or I get a chance to fit it


I didn't know the 20k PIWIS is available by mail order cable. I jest. 

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PIWIS cable is a £15 Chinese copy, thought it was worth a gamble.


The new purge valve arrived and I have fitted it before I needed to fill up again.


I checked for fault codes and it's still all clear.


Will see what happens at the next time I fill up......

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Fill up time today.


A couple of miles before hand I pulled over, switched off, removed the filler cap and replaced it. The car still drove perfectly.


Then I filled up and straight away it felt it was not quite right. Within half a mile it stuttered. I was close to home but it was far enough to confirm something was definitely up.


I won't trickle charge it tonight and see how it runs tomorrow.

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Hi, yes the voltage was 12.6v this morning first thing before starting and without the trickle charger connected.


A bit of a development, when I got home I connected the fault reader and it had an error saying the evap valve connection was open circuit, as to be expected. This was VW option on my reader.


I then cleared this and checked  the generic OBDII errors and got a message I have never seen before saying that there was a manufacturer specific error logged and it prompted me to select the manufacturer. Even though my reader doesn't support Porsche, Porsche was listed. When I selected Porsche I got the 2 following errors


P0098 Intake Air Temperature Sensor 2 Circuit High 

P1880 Please refer to vehicle service manual


I checked the connector to the Intake Air Temp Sensor and the contacts looked tarnished, and the orange connector seal didn't look in great shape either. I cleaned the contacts and ended up removing the seal completely as it wasn't sitting correctly, and filled the gap with silicon grease.


I also removed the sensor and was surprised to see fluid sitting inside the inlet pipework.


From a quick google P1880 is something to do with the transmission, not sure what - can anyone enlighten me?


Both codes cleared themselves.


I am going a bit further tomorrow so have put the trickle charger on as a precaution










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9 hours ago, DannyHoffman said:

Correction, I cleaned the connector for the turbo boost sensor

MAP sensor, it's sitting directly on top of the Y pipe. Sometimes it can get oil contamination, carb cleaner will sort that. Electrically though, brittle wires is also a common thing to see on these aging cars. I doubt this is related to the filling up and subsequent rough running that follows. 

P1880 doesn't seem to be genuine code or could be "transfer case disengagement" what ever that means or something totally different, more likely the reader your using is getting it's wires crossed I think. 


3/4 tank for me is the way to go, this will really point towards the evap canister and vent solenoid system. 

Can someone post the evap self check procedure? I wonder if the magic 5 miles relates to the cycle for leak test the system does periodically to check itself for leaks? I've searched for the info but didn't find. 

I'm thinking the tank is full and evap canister has got raw fuel in it, once the system identifies high enough rpm it opens the purge valve which sucks raw fuel through instead of vapor. You said you blocked off the purge valve and it still ran badly? So this would disprove this theory? 

Or the blocked evap canister and vent system when tank is full creates a vacuum in the tank and is highlighting a struggling left side primary fuel pump weakness. 

All speculation mind. 

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Now after having a better look from what I can see my turbo has three Intake Air Temperature Sensors, one directly on top of the Y pipe, and one either side in the intake tubing near the air filters. Are these all used, and if so which is which? My fault code stated sensor 2  had a problem.


To clarify I only blocked off the purge valve hose AFTER the car started to misfire following filling the tank, maybe I should have tried blocking it prior to filling up.



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Trickle charger theory is out the window. It said the battery was fully charged this morning but I am still getting an occasional misfire. No fault codes and I monitored the air intake temperature in real time whilst driving. It was giving expected readings with no glitches when the car misfired. My reader's real time monitoring only shows one air intake sensor.


As an experiment I've pulled the pipe off the purge valve on the tank side to see how it will run on the way home. My thinking being if the purge valve opens it will just suck in fresh air, not neat petrol

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I notice that you originally had P2177 and P2179 codes.


If after the next refuelling (to ¾ full), indications are that the evap canister is not the culprit, as another 'experiment' you may want to remove the MAF sensors and give them a spray cleaning. It's not too difficult a task, but it does call for a specialised MAF spray cleaner and particular care in carrying out the cleaning/drying process. 

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