Do your RPM's ever spike on the odd start up? The Cure is here!
#37
03-28-2011, 06:51 AM
I worry that the "fix" might be worse than the problem. It happens so infrequently and randomly for me that I hestiate to have the transmission dropped for this. So far no leaks and car runs fine. I'll wait until it's time for a clutch.
#39
03-29-2011, 06:09 AM
Pms sent guys.
Jhb you are right the fix can (and will) hurt the hip pocket....but the fix definately does "fix" it....if thats any consolation
.
And sbkim, i agree you "need" to get a tune, that way you will fry the clutch....but you'll be so glad you did even though your wallet wont appreciate it. Even though the car drives great with the stock tune and the right exhaust, with a "tune" its just plain ridiculous.
Jhb you are right the fix can (and will) hurt the hip pocket....but the fix definately does "fix" it....if thats any consolation
.And sbkim, i agree you "need" to get a tune, that way you will fry the clutch....but you'll be so glad you did even though your wallet wont appreciate it. Even though the car drives great with the stock tune and the right exhaust, with a "tune" its just plain ridiculous.
#40
03-29-2011, 10:22 PM
Stephen from IA once described a completely different reason for the start-up rpm spike that had to do with a defective engine coolant temp sensor. The sensor would register the wrong temp which told the ECU to add too much fuel for a cold start.
#41
03-29-2011, 11:47 PM
Not saying a defective engine coolant temp sensor wont cause it as i know from my own experience that an 02 sensor thats not fully snap locked will also cause a spike but i believe these situations are the rare exception...and not the rule. And will usually show up on the fault codes or throw a cel at one point whereas this problem won't. Did Stephen from( IA? ) post details? If so can you please link it for a read.
#42
03-30-2011, 06:37 AM
At first I thought the problem was temperature-related but after having experienced lots of cold starts in Colorado, I've never had the rpm spike to 3,000 rpms on a cold start, ususally 1,800 - 2,000. I typically get the 3,000 spike when the engine takes one more revolution to start which has made think the problem is more of a crank sensor issue. It happens so randomly for me but never with a hot engine so who knows the real culprit.
#43
05-01-2011, 05:34 AM
Hi fellow 997tt Members.
I started a thread on this a while back now asking you guys for advice about this very problem so now that i'm aware there is actually a fix, and this is a genuine problem and, "not normal", I wish to advise all those 997 owners out there that may be curious whats causing this rev up in their cars....and how to fix it.
There is a reason behind everything.
The exact cause of this problem is an incorrect gap between the the crank sensor and the passing marker....as it rotates past. The sensor is not set correctly within the specified tolerance. Evidently an inherent assembly issue.
As you may know the ecu must read and compute all sensors the moment the ignition key is turned and the starter motor begins to rotate the crankshaft. Voltage levels won't reach system requirements until the engine actually "fires up" so when the voltage is slightly down, as it often is after a period of being stationary, the sensor struggles to register the marker due to the incorrect gapping. (Like a spark plug which is incorrectly gapped too wide, more current is required to bridge the gap).
These occasions of "spiking" and, the frequency of these "rev up" spikes are often determined by how far away the marker is from the sensor after the engine is switched off. A weaker battery can also add to this problem.
For eg. If the marker has rotated just passed the sensor after the engine has stopped rotating, then upon restart, the starter motor must rotate the crank further for the marker to come back around past the sensor again to be registered. So, if the sensor is unable to read the marker due to incorrect gap (combined with the normal slightly lower voltage) the engine may sometimes continue to rotate without starting until the ECU is able to determine a start up ignition environment. The weaker the power the more rotations are likely to occur but once the ECU allows ignition the engine will fire up, the revs will momentarily spike, voltage is then restored to correct levels and then the ECU re registers the correct position of the crank sensor returning the rpm to correct idle speed.....all happening within a split second.
Now to the fix. And, some may not like it
. Gearbox must come off to access the sensor.....adjust sensor so it is gapped within the specified tolerance....gearbox back on again etc. IMO its probably best to do this when doing your clutch. You (may) be able to get P to fix it if it is happening ALL the time but that may very well depend on how far out of warranty you are, and the relationship you have with your dealer. Some cars can be worse than others and this is usually determined by just how far out of tolerance the sensor was installed to begin with....along with other factors such as the battery strength and condition. Its just a guess, but i think P figures that unless the problem is going to cause engine failure within warranty then they have little motivation to go to the trouble and expense of fixing it. The cure isn't that old so most dealers may not be aware of it.....although i am privy to the TSB number.
Hope this helps to settle this concern once and for all
I started a thread on this a while back now asking you guys for advice about this very problem so now that i'm aware there is actually a fix, and this is a genuine problem and, "not normal", I wish to advise all those 997 owners out there that may be curious whats causing this rev up in their cars....and how to fix it.
There is a reason behind everything
.The exact cause of this problem is an incorrect gap between the the crank sensor and the passing marker....as it rotates past. The sensor is not set correctly within the specified tolerance. Evidently an inherent assembly issue.
As you may know the ecu must read and compute all sensors the moment the ignition key is turned and the starter motor begins to rotate the crankshaft. Voltage levels won't reach system requirements until the engine actually "fires up" so when the voltage is slightly down, as it often is after a period of being stationary, the sensor struggles to register the marker due to the incorrect gapping. (Like a spark plug which is incorrectly gapped too wide, more current is required to bridge the gap).
These occasions of "spiking" and, the frequency of these "rev up" spikes are often determined by how far away the marker is from the sensor after the engine is switched off. A weaker battery can also add to this problem.
For eg. If the marker has rotated just passed the sensor after the engine has stopped rotating, then upon restart, the starter motor must rotate the crank further for the marker to come back around past the sensor again to be registered. So, if the sensor is unable to read the marker due to incorrect gap (combined with the normal slightly lower voltage) the engine may sometimes continue to rotate without starting until the ECU is able to determine a start up ignition environment. The weaker the power the more rotations are likely to occur but once the ECU allows ignition the engine will fire up, the revs will momentarily spike, voltage is then restored to correct levels and then the ECU re registers the correct position of the crank sensor returning the rpm to correct idle speed.....all happening within a split second.
Now to the fix. And, some may not like it
. Gearbox must come off to access the sensor.....adjust sensor so it is gapped within the specified tolerance....gearbox back on again etc. IMO its probably best to do this when doing your clutch. You (may) be able to get P to fix it if it is happening ALL the time but that may very well depend on how far out of warranty you are, and the relationship you have with your dealer. Some cars can be worse than others and this is usually determined by just how far out of tolerance the sensor was installed to begin with....along with other factors such as the battery strength and condition. Its just a guess, but i think P figures that unless the problem is going to cause engine failure within warranty then they have little motivation to go to the trouble and expense of fixing it. The cure isn't that old so most dealers may not be aware of it.....although i am privy to the TSB number.Hope this helps to settle this concern once and for all
Thanks!
#45
05-01-2011, 11:00 PM
The sensor is fixed (doesnt move or wear as such) so with this rev spike fault you should have experienced it well before now if it was the culprit....assuming your car is a few years old and has never done it before. However if the sensor is set on the max or beyond the max tolerance the revs will spike from time to time regardless whether the battery is new or not. The fix is to correct the sensor position so it is within tolerance.
If its never done it up till now then in your case it may be something else. Id check that out first before hassling the dealer with this technical report.
