Don't the .2 cars have 2 fuel pumps. A low pressure in-tank pump that feeds the high pressure DFI pump?

If so, 30vseconds of running is about the amount of fuel that would be in the lines between the 2 pumps. With an in-tank pump, vapor lock isn't really possible since the gas in the tank can't vaporize at the bottom, which is where that pump would be.

On 914s when the tank was in the front and the fuel pump in the back with the engine, you'd get vapor lock on really hot days where the fuel in the lines between the tank and pump would turn to vapor and then the pump at the engine couldn't pump the fuel in its gaseous state and the car would die. Moving the pump to the front, next to the tank, resolved the problem, and even if the gas in the liberal still vaporized, the liquid fuel being pumped from the tank would push it through.

Using that analogy, it almost sounds like the in tank pump is sometimes not being energized so it doesn't resupply the DFI pump and it does after 30 seconds. On the restart, the in tank pump is getting energized so it supplies fuel to the high pressure pump and all is well.

On my 09 DFI Cayenne, opening the drivers door primes the in-tank pump - you can hear it run. It will only do it the first time though unless 10 or 15 minutes pass, then it will do it again, but it won't do it on repeated door openings all in a row. Does the 997 use the same methodology? If so, start paying attention to hearing the pump prime when you open the door. If you don't hear it once, see if that's the time when the car dies.

If it doesn't work that way, you may still want yo investigate the wiring to the low pressure pump or that pump itself.

Good luck.

 

Interesting-had not discussed a duel fuel pump issue, makes sense. I wonder if there is a vapor lock between the two pumps on a hot day, and after being shut down for < 60 min it's still there....the tank pump is unable to supply the DFI. If that is the case, how does one solve it? Your idea about wiring though would not work since that would be independent of temperature, and being shut down for less than an hour. I am not sure how the 997.2 pump(s) interact, Need to do more research..

 

WAG: have you checked the clutch switch to see if something might be obstructing on an irregular basis?

 

A clutch switch problem might keep the car from starting, but shouldn't have any effect once it's already running, causing it to stall.

 

Possibility but something still isn't right. I drive in temperatures of low to mid 90"s six months out of the year, make frequent short stops like you describe and never had anything like this happen on two 997.2's with a total of almost 40,000 miles between the two cars. It does sound like it's fuel supply related though....somehow..

 

Very mysterious topic.
My 997.2 GTS PDK stalled on me last Friday. Went home after work, parked car in garage for about 15 mins or so...then took the car out, about a quarter mile / 3 mins or so (leaving the neighborhood) into the drive the car stalled (the light show came on)
I was on an up slope at a stop sign, when it was time to go, I pushed on the gas and it stalled. Put the car in P, then turn the key all the way left then restarted the car with out any issue. I have owned the car for almost 4 years (not a daily driver), that it's the first time this has happened.

 

Highpox, I had another thought on this. Since you say it only happens over 80 degrees, does that also mean it always happens with the A/C on or HVAC on Auto (which means the A/C is on)? Most cars have a switch or relay that elevates the idle slightly whenver the A/C compressor is running due to the additional load on the engine, to prevent it from stalling. Since you say it happens after driving when pushing in the clutch and coming to a stop, it almost sounds like the idle is falling too far and doesn't recover, so it stalls. If the 997 has a switch or relay for this purpose, it's possible that it is intermittent and not elevating the idle, or it's possible that the during the 1 in 20 times it happens, that the compressor was idling and just kicked on at the same time that the RPMs were falling and that extra load caused the stall. This is also why id doesn't happen every time. Or maybe the switch or relay is bad all the time, but if the compressor stays idling (you can feel the A/C clutch engage when it does), it doesn't happen because there wasn't additional load introduced. If the compressor was already running, it doesn't happen because the car is already adjusted to the additional load, but if it kicks on just as the revs are falling....

The other thing to think about when it's happening is how far are the revs falling when it stalls. Are you coming up to the stop from 3,000 RPM and pushing in the clutch or from 2,000 RPM and pushing in the clutch. The higher the RPM it's dropping from might make the potential for the stall higher also. What does your car idle at when warmed up? When you have the HVAC in Auto, do you see the tach change when you feel the A/C clutch engage - drop and then rise and be stable, hunt for a bit, drop a little and stay there?


chago996 - any recurrence of your issue since the new battery?

 

Any updates from the OP?

 

My A/C is basically always on. I never shut it off. It did it again last week, Temp was actually about 70F this time. I stopped for 15 min, started to drive..maybe at 5-10 mph so the tach was nothing. Pushed in the clutch and voila, all the lights came on. It just quits. The fix is easy, just key left, key right, starts up immediately. It does seem to do it when the tach is falling and the clutch in. It's never done it under a load. My idle warm in 700. Dead level. I think. The tach never bobbles when the compressor kicks in. I don't think it's a compressor load issue. It has to be a fuel delivery issue, maybe from the lp pump to the hp pump. A bad relay.. Something.

 

Once everything is warmed up and your idle is steady at 700, what happens if you hit the ECO button on your HVAC controller? Does the idle stay at 700 after a quick adjustment or does it then idle at 800 or so and stay stable there?

 

No it stays at the same RPM. I have never seen it drag down the idle. My old 944T was bad on that, but this 997.2 has been steady w/ A/C.

 

 

Did that issue reoccur?

 

 

Update since the last update: no issues, just the battery as talked about in August. It was the original battery since i bought the car in 2010. Since then, i have added another 5 or 6 k miles with no issues. 109k or so miles