Any ideas on this.
On my 04 CS (now 312 000 km) on a normal start there is a usually a "vroom" where the revs rise to about 1200 on startup before settling down to normal idle speed.

I noticed recently that occasionally, there was no rev rise or "vroom" on startup, in other words the engine would go straight to idle speed after start. This sounds a bit strange , but it got worse and once even sputtered a bit before starting (I had to give it a bit of throttle to get to engine running).

The interesting thing is that it seemed to happen only after filling up with petrol (gasoline), and the worst incident seemed to be after the tank was run down to about 18L left in the 100L tank.

so in summary

Filled up with 82L of petrol - sputtered to life
Filled up with about 50L - starts up at idle speed
otherwise normal start - revs up to 1200 then settles to normal idle

I haven't checked for fault codes yet, and the car seems to be running perfectly in all other respects, and the petrol filling could just be a coincidence.

Any ideas or comments ?

 

Makes me think fuel pump.. the pumps are supposed to pre-pressurize the injection rail before starting. If they didn't and the pressure in the rail dropped - a lack of fuel on startup might result in a lack of VROOM.

 

Fuel tank carbon canister ventilation valve is bad.
This one:

 

Don't think it's the pump.
Could be the fuel tank carbon canister thingy.
But definitely a fuel pressure issue.
I've also read a thread on Rennlist with a similar problem (just more severe) which was a cracked fuel line in the tank, which caused a drop in fuel pressure when the pump is not running.
If there is a small leak or crack causing the fuel pressure to slowly bleed off, would explain why it gets worse with a longer refuel, the car is simply parked longer. When the drivers door is opened the system is pressurized by the pump so there is no issue.
I will have to get hold of the fuel rail pressure tester to check if there is a pressure drop.
I did replace the left fuel pump a few months ago, so its possible that a pipe was damaged inside the tank during the operation.
Not looking forward to getting inside the tank again, as there is quite an octopus of pipes in there!

 

Plugged in the PIWIS and here are the fault codes:



I think the cam error is probably due to the poor sputtering start.

The evap code is possibly the carbon canister valve ?

I really expected to see a low fuel pressure code.

Good call Domino !

 

Poor start is one of the symptoms of bad purge valve.

 

So Porsche Centre Pretoria didn't have the purge valve in stock, so I had to wait about 2 weeks for the valve to arrive from Germany. Cost R1300 ($100).

Here is a pic of the location of the purge valve on the engine. It sits right next to the throttle body.




purge valve location




close up of purge valve

It wasn't a very difficult job, I would call it "fiddly".
Took me about 35 minutes , 25 of which was trying to remove the connection of the vent valve to the flexible pipe at the back of the engine, which refused to budge after moving the pipe clamp.





Rear connection of purge valve

I eventually cut of the old purge valve at the back, and removed the flexible pipe at the back completely at the quick connect, then removed the left over bit of purge valve pipe on the bench outside the car.






Old removed purge valve and new replacement

Threading the new pipe into position was a bit fiddly, but not really difficult.

I filled up the tank the morning after replacing the purge valve and the "vroom" seems to be back.

So thanks again to Domino for the good advice

 

I wrote a DIY on this replacement some time back for this forum, and for another one starting with R, ending with h...lol.
Look up purge evap valve and you shall find it. Not a half hour fix, but not bad either. Good luck.


Just found it on the forum here in case you wanted to see the purge valve DIY aka evap canister DIY. Click Here