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Unread 07-11-2010, 10:11 AM   #1
valley996
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Default RPM fluctuating while driving. Surge

I have a 1999 996 carrera tiptronic and it has a surge in engine speed between 1500 and 2200 rpms. The tac and engine speed goes up and down, in a steady rhytm. It does not do this while in park at the same rpms. I know this is hard to explain, but there are no check engine lights. It does this in all gears in the same range. It is smooth below and above the range I have listed. First thought was transmission, now I am not so sure.

I have gone to 3 mechanics. The Porsche mechanic did the PIWIS with the following results.

1. He did a 89757 internal malfunction test with piwis tester - none registered.
2. fluid level - good.
3. tested MAF - good
4. tested for power and ground on TCM module - good
5. removed torque converter lock up wire and test drove- good
6. checked fuel pressure - good
7. no codes in vehicle
8. solenoid circuits are intact and complete
HIS GUESS: He said the main line pressure was checked with a piwis tester and it it showed the main line for transmission fluid control loses pressure on and off which is a sign of a weak solenoid.

What I have done:

1. Cleaned the TCV ( very dirty, also looking inside of it the flap that opens and closes is not fully opened or closed. Is
this normal?)

2. Unplugged the MAF and drove, no changes

3. Cleaned the throttle body.

NOTE: What is happening is the car rpm's are jumping up and down as if I am pressing the gas pedal and letting off, but it is doing it on it's own. It does get worse on a grade. It does it while crusing between 1500 and 2500 rpms, when the car has no need to shift, which leads me to believe it may not be a transmission issue as was though early on. I can use the manual mode of the tiptronic in all gears and it does it in that range. Note: If the car is in Park, there is no problem in that same range when I rev the engine, it's only when moving. Also, as a reminder I have no codes with the PIWIS or Durametric tester.

I would appreciate any help. Thanks
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Unread 07-11-2010, 10:12 AM   #2
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There is a video of a a 2002 Audi on Youtube that does the same thing as mine, if you care to watch.


Thanks Again,

Aaron

http://www.youtube.com/watch?v=ZhfeWfLuDQo
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Unread 07-12-2010, 10:43 AM   #3
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Unhappy Recalling

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Unread 07-12-2010, 08:42 PM   #4
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Big help! Thanks
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Unread 07-20-2010, 08:54 PM   #5
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I have no clue what the problem might be, but I'll give your thread a bump.
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Unread 04-18-2014, 01:05 PM   #6
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Default Fluctuating RPM

Boy would I be interested what you have found out. My 00 996 C2 TIP is doing the same thing. It is my last bug to work out. Mine falls in the same RPM range but is more of a leap in RPM. Similarly my opinion is Transmission so I had the fluid changed but no change. My second thought is something with the Vario Cam timing. Also I have two of these C2's the other is a manual and has no issues, however comparing the two cars makes me think the Tip equipped car has had some reprogramming since it revs faster and seems more powerful. I also think maybe the leap may be a programming issue? As you can see I am still guessing. Any ideas?
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Unread 05-28-2014, 10:58 PM   #7
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Does it do the same thing when it is in "Manual" or "Sport"?
There is a *Brit show that flips cars. They had a Boxster that did the same thing but more so in "Auto". They dropped the trans pan and changed the filter assy. That fixed the surging.
Wheeler Dealers
Season 12 episode 4 Porsche Boxster S
http://www.youtube.com/watch?v=45L6FDJaeQk
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