Engine Stumble on Roll Out
08-12-2014, 08:40 AM
#46
Here is a thought related to that- does your PSE button actually work? The vacuum valve that controls the exhaust has been known to fail. From what I know of the PSE, when it is on the valves are open at idle, closed until 3-4k and then open again. If the valves failed, they would be open the whole time, which at that low rpm would reduce torque maybe just enough to throw off the PDK, just like what is happening with the aftermarket xpipe.
08-12-2014, 09:59 AM
#47
Has anyone tried putting the car in sports plus and manual mode to see if that would alleviate the problem. I ask because that because it would dial back the PSM . Everyone here is a PDK owner(this thread}? I do not have PSE but I assume there is enough difference in sound that it would be obvious if it were activated.
08-12-2014, 05:36 PM
#48
Rennlist Member
Has anyone tried putting the car in sports plus and manual mode to see if that would alleviate the problem. I ask because that because it would dial back the PSM . Everyone here is a PDK owner(this thread}? I do not have PSE but I assume there is enough difference in sound that it would be obvious if it were activated.
08-12-2014, 06:45 PM
#49
Race Car
07-26-2015, 11:56 PM
#53
Racer
Join Date: Apr 2015
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Glad I um bought my car with 2600 miles on it likely just driven down the driveway. Mine is doing it exactly as described in these posts and 6speed. Just read 60 pages of literally nothing.
07-27-2015, 12:08 AM
#54
Instructor
Subscribed. I'm looking forward to the resolution since mine does the exact same thing since day 1. I always wondered how this car can do 0-60 under 4 seconds while hesitating like that...
I have a 2014 991S PDK. It's developed an issue that I likely need to just go to the dealer for, but wanted to ask if it was common.
Occasionally from a dead stop, when I apply the gas the RPMs rise and then the car stumbles as if on a manual car you either let the clutch out too fast or gave it too little gas. Of course I compensate by giving more throttle, then once the engine recovers it revs very quickly.
I can't really determine if it's a cold/hot thing. I've had it happen in normal and sport mode. It's happened when I'm trying to smoothly accelerate and when I've given ~1/2 throttle.
It's kinda dangerous. A couple of times I've pulled out with plenty of distance to cross a one way street by my house, but the car bogs, hangs for a second or two, THEN goes. Which when your car has moved into traffic, is not a fun thing to happen.
Is this a common issue?
UPDATE
I finally had time to bring the car to the dealer.
Turns out my fears about the issue not being replicatable were unfounded. The dealer definitely identified the issue. At first, they questioned me about where I bought gas. They also indicated that they had tested the octane. I buy mostly Shell and of course always use the good 93 we get in Texas.
The service writer first took a stab at replacing wheel speed sensors. That was yesterday. I called today and they said they're waiting for a crankshaft sensor, so I'm thinking the wheel speed sensors didn't do the business.
The sensor won't be available at the dealership until Monday and I'm out of the country until Wednesday. I'll update this thread as soon as I get the car back.
Occasionally from a dead stop, when I apply the gas the RPMs rise and then the car stumbles as if on a manual car you either let the clutch out too fast or gave it too little gas. Of course I compensate by giving more throttle, then once the engine recovers it revs very quickly.
I can't really determine if it's a cold/hot thing. I've had it happen in normal and sport mode. It's happened when I'm trying to smoothly accelerate and when I've given ~1/2 throttle.
It's kinda dangerous. A couple of times I've pulled out with plenty of distance to cross a one way street by my house, but the car bogs, hangs for a second or two, THEN goes. Which when your car has moved into traffic, is not a fun thing to happen.
Is this a common issue?
UPDATE
I finally had time to bring the car to the dealer.
Turns out my fears about the issue not being replicatable were unfounded. The dealer definitely identified the issue. At first, they questioned me about where I bought gas. They also indicated that they had tested the octane. I buy mostly Shell and of course always use the good 93 we get in Texas.
The service writer first took a stab at replacing wheel speed sensors. That was yesterday. I called today and they said they're waiting for a crankshaft sensor, so I'm thinking the wheel speed sensors didn't do the business.
The sensor won't be available at the dealership until Monday and I'm out of the country until Wednesday. I'll update this thread as soon as I get the car back.
07-27-2015, 12:57 AM
#55
07-27-2015, 04:27 PM
#56
Rennlist Member
Darn... I must have missed the class which explained how mechanical conformity issues could lead to binary on-off behaviour... Seems so counter intuitive... But as it's you I will trust you with my prize possessions in future and break the next one in like I stole it... with cognitive dissonance of course...
07-27-2015, 04:38 PM
#57
07-27-2015, 04:47 PM
#58
Rennlist Member
I'm coming up on the 35K mile mark so I added some Techron fuel injector cleaner on my last refuel so I can go through the tank before my next oil change.
Drove all weekend (400 miles) in sport mode with no hesitation and power on demand..... the car felt fantastic.
For those with hesitation try some and see if it goes away.
Does anyone know of an upgrade for the 991's coil packs or spark plugs?
Drove all weekend (400 miles) in sport mode with no hesitation and power on demand..... the car felt fantastic.
For those with hesitation try some and see if it goes away.
Does anyone know of an upgrade for the 991's coil packs or spark plugs?
