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up4speed

2001 996 TT idles rough for a few seconds when started cold.

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I have a little more info.  I hooked up my OBD2 reader so I can read the throttle position sensor readings.  Most readings made sense, but there was a specific range that may possibly be an issue.

When the throttle was not pushed, it read 3.something% open, when it was floored, it read 100% open, so this made sense.  Then I pushed it in various positions and held it.  It seemed like rock steady readings all across the board, except for the high 30's to high 40% range.  In that range, the % would sometimes fluctuate a very slight amount. It fluctuated maybe .2 or .3%.  This occurrence was very random.  Sometimes it would lock in immediately, other times it would fluctuate up and down for a few seconds, then lock in. 

Is it possible that this may cause that surging that I get randomly?  Or is it too slight of a variation to affect/feel anything?
I'm going to take the car out today with the reader hooked up to see if I can get a pattern going between the reading and the surging.  

I'll check back here when I'm done.

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I just got back from my drive.  I drove about 25 miles and I couldn't get it to surge. Unfortunately It's very unpredictable and I don't know how to duplicate it. 

The only things that I noticed that are very distinct were that the car starts perfectly when cold and is very smooth, then there is a brief dip in the RPM's, then it picks back up and that's precisely when it runs rough.  It's evident in the video when it does that dip shortly after starting.  When it's running a little rough, if I hold the RPM's at 1,800, the car will then run VERY rough. (once it warms up, it doesn't feel significantly rough any more)

 

The other things I noticed were regarding the readings on the live view of the OBD2 reader.  I kept an eye on the TP%, every now and then when I gave it 1/4 to 1/2 throttle and held it steady, the reading would shoot up to 92%-100% for no reason, then settle down to a proper reading after a second or two.  While it did this, I didn't notice any drivability problem, so I wonder if it's just a normal occurrence of the car just doing the math?

I also noticed that there are two fuel trim readings that I don't understand or know what they are, but they have values that never changed throughout the whole drive.  The two readings are:

SHRTFTB1S2 (%) - N/A

SHRTFTB2S2 (%) - 99.2

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SHRTFTB1S2 =short term fuel trim bank1 sensor 2

 

SHRTFTB2S2 =short term fuel trim bank2 sensor 2

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What spark plugs were installed? Maybe it's just a matter of a cold fouled plug? Where they torqued correctly? 

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SHRTFTB1S2 =short term fuel trim bank1 sensor 2

 

SHRTFTB2S2 =short term fuel trim bank2 sensor 2

 

I wonder if those sensors are not applicable to my car since the values never change?  The other fuel trim readings seem normal.  If you take a look at post #5, I took a photo of the diagnostic screens that my reader has when it's hooked up with the engine off. It shows the above two readings for the sensors that stayed fixed as well as the other fuel trim readings that seemed to be changing appropriately with the diving conditions.

Are the readings for STFTB1S2 and STFTB2S2 supposed to change?

What spark plugs were installed? Maybe it's just a matter of a cold fouled plug? Where they torqued correctly? 

The spark plugs used on the car (according to the receipt) are:

 (7410) FR6LDC  (I think he meant to write LDU not LDC)

Those should be correct according to the manual, however I don't know the torque they used since it was a shop that did it before I owned the car.  They were done 3 years and 7,000 miles ago.

 I thought that I read somewhere that cars with a performance tune (I have the Ultimate Motorwerks tune) eat through spark plugs much quicker and it may help to go with one step colder.  Is there truth to that?

Edited by up4speed

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Have you tried throttle body recalibration? i.e., turn key to last position before cranking and leave it there 60s (foot off the gas pedal). Then remove key.

 

Also did you check for any air leak (smoke test) on the engine?

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SHRTFTB1S2 =short term fuel trim bank1 sensor 2

 

SHRTFTB2S2 =short term fuel trim bank2 sensor 2

 

I wonder if those sensors are not applicable to my car since the values never change?  The other fuel trim readings seem normal.  If you take a look at post #5, I took a photo of the diagnostic screens that my reader has when it's hooked up with the engine off. It shows the above two readings for the sensors that stayed fixed as well as the other fuel trim readings that seemed to be changing appropriately with the diving conditions.

Are the readings for STFTB1S2 and STFTB2S2 supposed to change?

What spark plugs were installed? Maybe it's just a matter of a cold fouled plug? Where they torqued correctly? 

The spark plugs used on the car (according to the receipt) are:

 (7410) FR6LDC  (I think he meant to write LDU not LDC)

Those should be correct according to the manual, however I don't know the torque they used since it was a shop that did it before I owned the car.  They were done 3 years and 7,000 miles ago.

 I thought that I read somewhere that cars with a performance tune (I have the Ultimate Motorwerks tune) eat through spark plugs much quicker and it may help to go with one step colder.  Is there truth to that?

 

 

Couple of thoughts:  Yes, most "tuned" turbo cars benefit from running at least one step colder plugs.  Secondly, have you tried measuring the same fuel trims but using a Porsche specific scan tool ( Durametric, PST II, PIWIS)? 

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Have you tried throttle body recalibration? i.e., turn key to last position before cranking and leave it there 60s (foot off the gas pedal). Then remove key.

 

Also did you check for any air leak (smoke test) on the engine?

I didn't do a smoke test, but I'll bring it to the dealer if it comes to that.

I didn't even know about the throttle body calibration, but I guess I'll do it.  It can't hurt.  I probably "accidentally" did it when I hooked up the scan tool for the photos in my prior post.  I hooked the scan tool up, turned key to on position, then shut it off.  The ignition was on for several minutes before turning off, so I'm pretty sure it was reset.

 

 

 

 

SHRTFTB1S2 =short term fuel trim bank1 sensor 2

 

SHRTFTB2S2 =short term fuel trim bank2 sensor 2

 

I wonder if those sensors are not applicable to my car since the values never change?  The other fuel trim readings seem normal.  If you take a look at post #5, I took a photo of the diagnostic screens that my reader has when it's hooked up with the engine off. It shows the above two readings for the sensors that stayed fixed as well as the other fuel trim readings that seemed to be changing appropriately with the diving conditions.

Are the readings for STFTB1S2 and STFTB2S2 supposed to change?

What spark plugs were installed? Maybe it's just a matter of a cold fouled plug? Where they torqued correctly? 

The spark plugs used on the car (according to the receipt) are:

 (7410) FR6LDC  (I think he meant to write LDU not LDC)

Those should be correct according to the manual, however I don't know the torque they used since it was a shop that did it before I owned the car.  They were done 3 years and 7,000 miles ago.

 I thought that I read somewhere that cars with a performance tune (I have the Ultimate Motorwerks tune) eat through spark plugs much quicker and it may help to go with one step colder.  Is there truth to that?

 

 

Couple of thoughts:  Yes, most "tuned" turbo cars benefit from running at least one step colder plugs.  Secondly, have you tried measuring the same fuel trims but using a Porsche specific scan tool ( Durametric, PST II, PIWIS)? 

 

I didn't have access to the Porsche specific tool, so I only used my OBD2 reader.  I will add that to the list of things for the dealer to do if I hit a dead end.

Within a week all the stuff I ordered will have arrived.  By next week I will have new motor mounts, transmission mount, MAP sensor and MAF sensor and Techron gas treatment.  I'm hoping that it takes care of the rough idle, clunk noise when dropping transmission to 1st and the random surging issue.  If that stuff doesn't work, I'm also ordering the handheld programmer that is needed to put my car back to a stock program.  I want to put it back to stock for troubleshooting, I don't want to chase my tail just to find out it is a simple as a tuning issue.  The symptoms are not that severe, so I would be fine with it if I knew that the issues were definitely stemming from the tune, and not a legitimate problem. However if it isn't the tune, I definitely want it fixed!

Edited by up4speed

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Today I made this contraption so I can pressure check the engine.  I will post my findings as soon as I test it. 

post-17066-0-41123400-1428039618_thumb.j

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I wanted to give you guys a follow up on my progress with my troubleshooting. I pressure tested the intake today with the tool that I made shown above. It worked great!  I used only about 7-10 psi and unfortunately/fortunately (maybe it will fix the issues!) I had a leak.  I found it with soap and water and I tried to use an inspection camera to get a better look but I still couldn't determine which part it is.  The leak was from the joint of the F-pipe where it goes into the blowoff valve.  Unfortunately it was the deeper valve, the one I can't reach! It figures, ughhh

I can't tell if it's an issue with the rubber hose, or a crack in the valve. It appears to be leaking at the seam of the connection.
What are the symptoms of a leak at that location? Would it cause the rough idle issues, or surging?

Is there a way to remove the assembly (F pipe and valve) to allow me to inspect it more carefully so I can determine what needs to be done?  I can't even get my hand in there!  It seems impossible.  I have to assume that the engine needs to be lowered a little?
Any help would be appreciated.

 

I also changed the MAF, MAP and the transmission mount today.  It all went smoothly, however, I didn't test drive it yet because I wanted to fix the air leak first.  Once that's fixed, I will also change the motor mounts.  I will report back with the results at the end with hopes that I can help another person in the future.

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Here's a document from Rolfjahn on 6speed to help you lower the engine and give you more access to the F pipe…: 

 

Here's a video to help you with the motor mounts. Remember the square hole on the engine cradle... The base of the engine mount is also square and has to enter this square recess….https://www.youtube.com/watch?v=dBL2-iy6li4https://www.youtube.com/watch?v=dBL2-iy6li4

 

Thanks guys, I'm going to take a crack at it today. 

I'll post the results

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I finally found the actual cause of the leak!!

It was frustrating to find because initially the air seemed to be coming from the F pipe joint of the forward blowoff valve.  Well after taking it all apart and inspecting, I found nothing wrong. So I re-assembled it being very careful that the clamps were straight and everything was pushed on tightly, and unfortunately it STILL leaked!!!  I then took it apart again and used regular worm gear hose clamps and reassembled again, it still leaked!  I had to take it apart a 3rd time, this time really pissed that the car was defeating me. Before I took it apart a 3rd time, I decided to lower the engine a little more to give me even more access since I was determined to find the problem.  This time I reached in all the way and after pressurizing it, I realized that it was the Y-pipe under the blowoff valves! It was difficult to find because the hole aimed the air right at the F-pipe connection and made soap suds (I used a soap/water mixture to help me find the hole) on the F-pipe instead of the source (It's not like I could see the whole Y-pipe with everything hooked up anyway).

The craziest part is that the Y-pipe looked perfect even after I removed it!  The only way I was able to see the hole is if I stretched the Y-pipe apart, see the photo.

Well I ordered the part and will follow up with an update after it's in.  It will probably take about a week.

If there is any good news about this story, it's that I can now change blowoff valves in about 15 minutes flat without too much trouble! Lol

post-17066-0-54647500-1428281597_thumb.j

post-17066-0-56870200-1428281882_thumb.j

Edited by up4speed

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Good job! That's why they use smoke :) Hope that fixes the idle problem.

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I finished all the work on the car.
just for a summary, here is everything I did to it so far:

Changed fuel filter
Changed air filter
Cleaned throttle body
Put Techron in the tank
Replaced MAF sensor
Replaced MAP sensor
Changed transmission mounts
Changed engine mounts
Pressure checked intake and replaced V-pipe with hole in it (as shown above)
Re-synchronized throttle after restoring battery power

I'm happy to report that the car seemed smoother, the transmission didn't
kick when dropped into 1st gear ( tiptronic), and the boost built faster and
held constant boost as I stayed on the throttle and didn't dip off like before.

There is some bad news though.  After I finished all the work, I let it sit over night and started it again today and it still had the same exact cold start characteristic that it had before any of this work.  It idles very smoothly at about 1,200rpm, then after a few seconds, the engine dipped down in rpm's, then back up.  It then runs rough and feels like an off balance motor until it warms up a little and the rpm's drop to approx. 800 where it stays when warm and idles smoothly.

Another issue I noticed on the first drive I took, was a knocking sound which sounded like detonation
under load (~3/4 throttle acceleration) up a slight hill. I think I remember hearing it in the past, but it was so slight that I second guessed it.  Now that the Turbo is pushing more boost, I feel like it made the noise a little more pronounced.  It sounded like
it was coming from behind me on the drivers side and did it for a second or
two, then went away.  I didn't feel any loss of power like the knock sensor
was retarding the timing though.  I took it for a drive again the next day (today), and it didn't do it.  I took the same route and tried to match the same exact driving that I did yesterday.

Just for the record, I have a fresh tank of Shell 93 octane in
it.  Is there anything else for me to check? 

 

Edited by up4speed

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93? In sweden i think the book says min.95 but we dont have 93. Only 95, 98 a v-power(99?). I drove my old boxster i used to have on 98..

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I'll be changing the wideband O2 sensors this weekend. I don't know if it will tackle the last remaining possible issues or not, but I just want to do it for maintenance.

Are there any hints or tricks that will make replacing them easier, or is it straight forward?

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I'll be changing the wideband O2 sensors this weekend. I don't know if it will tackle the last remaining possible issues or not, but I just want to do it for maintenance.

Are there any hints or tricks that will make replacing them easier, or is it straight forward?

 

If your O2 sensors were causing the problem is would show up as a fault or as poor O2 sensor waveforms.

Best to put a Porsche PIWIS tester on the car and monitor it.

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I'll be changing the wideband O2 sensors this weekend. I don't know if it will tackle the last remaining possible issues or not, but I just want to do it for maintenance.

Are there any hints or tricks that will make replacing them easier, or is it straight forward?

 

If your O2 sensors were causing the problem is would show up as a fault or as poor O2 sensor waveforms.

Best to put a Porsche PIWIS tester on the car and monitor it.

 

I would do that if I had access to the PIWIS tester.  I figured if I had to pay for that testing, I might as well change the O2 sensors since they are 14 years old, and cheap.  I don't mind spending a little money to have a lot of the common failure parts taken care of.  Even if it doesn't fix what I perceive as a problem, The car will at least have a lot of new parts that I shouldn't have to worry about for a long time.

If The O2 sensors don't fix the problem, I'll also replace the spark plugs.  This way I know that it has the proper plugs, gapped properly.  If after all that, I still feel that it's "not right", I will give up and either ignore the remaining "issues", or take it to a Porsche mechanic.

I really don't mind doing the work, it's a hobby for me and I have a lift which makes most jobs easier. Of course, I also like to learn about my cars.

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Excuse my rant...Just be aware that every time you go and change parts out you increase the chance of not re-assembling correctly (loose fittings, etc.).  Also your approach doesn't lend itself to actually understanding the issue.  The methodology of having a symptom, taking an action (e.g., replacing parts) and having the symptom go away (since there really is no measure of your issue....just feel) and concluding it was the last action you took (the "fixed" the problem) is not even close to a suitable methodology for understanding the cause.

 

The sensors are not a performance item...they either work or they don't. Replacing them early just costs you time and money, and proves nothing...but of course it is your time and money so do whatever you wish.

 

Get Durametric code reader (it will come in useful since you like to tinker).  And then get some actual data on the car's performance (like suggested by Loren).

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Excuse my rant...Just be aware that every time you go and change parts out you increase the chance of not re-assembling correctly (loose fittings, etc.).  Also your approach doesn't lend itself to actually understanding the issue.  The methodology of having a symptom, taking an action (e.g., replacing parts) and having the symptom go away (since there really is no measure of your issue....just feel) and concluding it was the last action you took (the "fixed" the problem) is not even close to a suitable methodology for understanding the cause.

 

The sensors are not a performance item...they either work or they don't. Replacing them early just costs you time and money, and proves nothing...but of course it is your time and money so do whatever you wish.

 

Get Durametric code reader (it will come in useful since you like to tinker).  And then get some actual data on the car's performance (like suggested by Loren).

Good points Wross.  You are definitely speaking logically.....however, I'm still going to change the O2 sensors (14 years old) and spark plugs (>4 years old) as a last ditch effort, plus the plugs should be replaced anyway at 4 years according to owners manual.  If everything that I have done does not correct 100% of the issues that I perceive (I may be wrong) as problems, I will definitely look into getting the proper software, or taking it to a Porsche mechanic. 

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I am in the process of changing the plugs and wideband O2 sensors.  Do I dare say that it's actually FUN?  I may be a little twisted sometimes, LOL
So far everything went smoothly except for the fact that I snapped off the locking clip on one of the coil pack connectors. Be careful of these, they probably get brittle from heat cycling and age.
The worst part is that my production came to a halt until I get a replacement connector.  Thankfully I have a friend that may have an old harness lying around and he may be able to give it to me tomorrow so I don't get delayed a few days waiting for it to come in the mail. 
The interesting part is that EVERY SINGLE plug was loose!  Most were removed with light wrist pressure.  The color of the plugs were all a nice light brown color, but the threads looked like they had a heavy grease on them.  I'm not sure if that was anti-seize used by prior mechanic, or if it was just accumulation from blow by on the loose plugs.  I think that the mistake that the prior mechanic made was to torque the plugs only once.  A lot of people don't realize that the o-ring compresses and the plug will loosen up if it is not re-torqued a few times.   I did them at least 3 times each with a few minutes in between each time. Hopefully that will prevent them from loosening in the future. 
I have a good feeling that the loose plugs may have causes the idle issues that I'm having, and maybe even the sound of a misfire under load.  I'm not having a good feeling about the misfire sound because I'm thinking that it may just be a rattle since there is no code or loss of power or drivability when it does the noise.  In addition, it was very random and I was not always able to duplicate, so I will cross my fingers on this.  I also checked the brackets near the middle plugs just in case they are ready to fail, but they looked brand new (very low miles on the car).
At this point, I'm VERY anxious to road test her to see if there is a difference.
It should be ok to start the car before I install the bumper (after everything else), just to make sure that it is ok, right?  I would hate to have made a simple mistake forgetting something, just to find out after EVERYTHING is all back together!  I'm sure that I did everything correctly, but I'm human so you never know.
Oh, one more question.  Do you guys think that I should disconnect the battery to reset the computer to accept the new plug and O2 sensor parameters, or does it not matter?

 

Edited by up4speed
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I am in the process of changing the plugs and wideband O2 sensors.  Do I dare say that it's actually FUN?  I may be a little twisted sometimes, LOL

So far everything went smoothly except for the fact that I snapped off the locking clip on one of the coil pack connectors. Be careful of these, they probably get brittle from heat cycling and age.

The worst part is that my production came to a halt until I get a replacement connector.  Thankfully I have a friend that may have an old harness lying around and he may be able to give it to me tomorrow so I don't get delayed a few days waiting for it to come in the mail. 

The interesting part is that EVERY SINGLE plug was loose!  Most were removed with light wrist pressure.  The color of the plugs were all a nice light brown color, but the threads looked like they had a heavy grease on them.  I'm not sure if that was anti-seize used by prior mechanic, or if it was just accumulation from blow by on the loose plugs.  I think that the mistake that the prior mechanic made was to torque the plugs only once.  A lot of people don't realize that the o-ring compresses and the plug will loosen up if it is not re-torqued a few times.   I did them at least 3 times each with a few minutes in between each time. Hopefully that will prevent them from loosening in the future. 

I have a good feeling that the loose plugs may have causes the idle issues that I'm having, and maybe even the sound of a misfire under load.  I'm not having a good feeling about the misfire sound because I'm thinking that it may just be a rattle since there is no code or loss of power or drivability when it does the noise.  In addition, it was very random and I was not always able to duplicate, so I will cross my fingers on this.  I also checked the brackets near the middle plugs just in case they are ready to fail, but they looked brand new (very low miles on the car).

At this point, I'm VERY anxious to road test her to see if there is a difference.

It should be ok to start the car before I install the bumper (after everything else), just to make sure that it is ok, right?  I would hate to have made a simple mistake forgetting something, just to find out after EVERYTHING is all back together!  I'm sure that I did everything correctly, but I'm human so you never know.

Oh, one more question.  Do you guys think that I should disconnect the battery to reset the computer to accept the new plug and O2 sensor parameters, or does it not matter?

Here are some photos of my fun:

 

 

You do not need to reset anything for the car to accept the new plugs and O2 sensors.

 

Nice shop layout, by-the-by. :thumbup:

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