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Fault codes diagnosis help...


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I have a 2000 Boxster with fault codes P1128 and P1130.  I know these have been covered extensively in this forum and cleaned the MAF only for the codes to come back.  I am looking for a fellow Renntechian that lives around Chicago to help diagnose the actual issue.  I will buy lunch and a few beers.

T

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First see if you can clear the codes to see if them come back.

 

The codes mean:

 

P1128 Oxygen Sensing Adaptation, Idle Range, Bank 1 Above Limit
P1130 Oxygen Sensing Adaptation, Idle Range, Bank 2 Above Limit
Possible fault causes:
Incorrect signal from MAF sensor
Intake air system leaking
Fuel pressure too low
Volume supply of fuel pump too low
Fuel injectors fouled
Exhaust system leaking

 

This tells you that your O2 sensors are working and they are telling you something.  I would always start with the most obvious and also least expensive.

 

Do 1-3 below and clear the codes again to see if they return.

If that doesn't work then clear the codes after 4, then 5, then 6.  MAF is most expensive.

 

1. Clean your air filter and/or replace it.

2. Clean your MAF.

3. Vacuum Leak could be a bad oil cap (if you have a yellow one replace it).

4.  Check your throttle body and "J" tube for excess oil and clean thoroughly.

5.  If in there is a lot of oil and your car smokes more than usual at startup, I would suspect a bad AOS, test and replace.

6. Replace MAF

 

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Thank you K....I have done 1 and 2.  I do have a yellow oil cap so I will go ahead and replace.

Today, in addition to P1130 and P1128 I get two "pending faults" P1126 and P133.  

 

Does this point to a more particular issue?

 

T

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I have a 2000 Boxster with fault codes P1128 and P1130.  I know these have been covered extensively in this forum and cleaned the MAF only for the codes to come back.  I am looking for a fellow Renntechian that lives around Chicago to help diagnose the actual issue.  I will buy lunch and a few beers.

T

AOS is suspect... What happens when you remove the oil fill cap while the motor is running (warmed-up at idle)?

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Its probably indicating a bad MAF.  I would still do #4 and #5 on post #2 above.  If you need info on a AOS test, let us know.  I also wouldn't totally eliminate a faulty oil fill tube.  What does your engine bay look like.  When my AOS went it also created a cracked center oil filler tube. 

 

Your car has three oil filler tubes that connect together from the rear trunk fill location to the 3rd tube at the top of the engine close to the fire wall .  It is usually the middle tube.  Each tube is about $30 US. Be careful if you replace the middle tube as the 3rd (last) tube as little ears that bolt to the top of the engine & hold it in place.  The ears are easy to snap off by forcefully moving it while replacing the center tube. Breaking those ears will cause you to replace the third tube also.

 

I'm not sure if you are the original owner or if the previous owner had accurate service records.  Depending on that and how many miles your MY2000 Boxster has, you may end up to doing everything.

Edited by kbrandsma
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Thank you both.....will venture in over the weekend and let you know....Jager, what should I be looking for with the oil cap removed at idle?

kbrandsma, not original owner...car has 60,000 miles....engine bay dirty but I do not believe oily.....will take again a look now that I know what I am looking for.

 

T

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If the AOS is original to the car and has never been replaced, (14 years and 60K miles) its time to replace.

 

To test for a faulty AOS it can be as simple as starting the car and while at idle, try and remove the oil cap in the rear trunk.  A faulty AOS creates a stronger than required vacuum and will make the oil cap very difficult to remove.  With the engine off, you should also take the tube (J tube) off of the AOS that connects to the throttle body and see how much oil is in the tub.  I would suspect some or a film (that's normal) but if it's filled with oil the AOS is definitely gone.  Having the J tube off will also give you an idea how much oil went from the AOS through the J Tube and into the throttle body. Also, with a faulty AOS the middle oil fill tube collapses and expands and eventually may crack as it gets older and brittle, so always look at that as well.

 

A more sophisticated (but inexpensive) testing tool called a slack tube manometer can be used to test for a faulty AOS.  How to build one can be found on a DIY post by logray here on the Renntech Board  PRESS HERE

 

Photo of logray's setup.

slacka.jpg
 

 

Here is a link to Pedro's site regarding the AOS.  It explains how to remove the J tube, clean the throttle body and ICV and maybe eventually replacing the AOS.  PRESS HERE

 

Here is a link to a Pelican Technical Article on replacing the AOS  PRESS HERE

 

If you do end up replacing the AOS, there are some shortcuts you can take during removal to make the job a little easier.

Edited by kbrandsma
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3. Vacuum Leak could be a bad oil cap (if you have a yellow one replace it).

 

  

I have one of those yellow oil filler caps.  I never did like it as the seal is just a "loose" O-ring stuck in there.  Really cheap.

 

It's actually more orange than yellow (compared to dipstick handle).  Part # 996 107 350 52.  Should I replace this?

 

The replacement appears to be part # 996 107 035 52 which is black plastic with a green seal.

Edited by Dennis Nicholls
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I have a 2000 Boxster with fault codes P1128 and P1130.  I know these have been covered extensively in this forum and cleaned the MAF only for the codes to come back.  I am looking for a fellow Renntechian that lives around Chicago to help diagnose the actual issue.  I will buy lunch and a few beers.

T

AOS is suspect... What happens when you remove the oil fill cap while the motor is running (warmed-up at idle)?

 

Removed the oil cap at idle and running temperature.  Some rough idle but not to the point where the car would stall.

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I have a 2000 Boxster with fault codes P1128 and P1130.  I know these have been covered extensively in this forum and cleaned the MAF only for the codes to come back.  I am looking for a fellow Renntechian that lives around Chicago to help diagnose the actual issue.  I will buy lunch and a few beers.

T

AOS is suspect... What happens when you remove the oil fill cap while the motor is running (warmed-up at idle)?

 

Removed the oil cap at idle and running temperature.  Some rough idle but not to the point where the car would stall.

 

Look at the RPMs after you remove the oil fill cap, did the RPMs drop or increase? If the RPMs drop, the motor stuggles to idle, and the oil fill tube sounds like a Shop Vac, then the AOS needs to be replaced. If the RPMs actually increase a little then your AOS is probably OK.

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Replaced the oil cap and I got noticeable performance improvement.  The faults are still showing up after I scan for errors (P1128, P1130, P1126, P1133),

Do I need to clear the codes and let it run and see if they come back?

 

Also, I get some smoke when I start the car when the car is sitting for a couple of days...otherwise, none or very little. Can it still be the AOS?

 

T

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Replaced the oil cap and I got noticeable performance improvement.  The faults are still showing up after I scan for errors (P1128, P1130, P1126, P1133),

Do I need to clear the codes and let it run and see if they come back?

 

Also, I get some smoke when I start the car when the car is sitting for a couple of days...otherwise, none or very little. Can it still be the AOS?

 

T

Yes you will have to clear the codes, they will not clear automatically. If the codes come back AOS is suspect. When you remove the oil fill cap (warm engine) does the oil fill tube sound like a shop vac? Did the RPMs drop (look a tach)?

Edited by Jager
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After eliminating AOS as culprit, a potential intake air leak can be caused by faulty vacuum lines (see diagram below).

 

Getting in there with top and front hatch removed is fiddly but doable. I have had success replacing old & brittle vacuum lines with generic vacuum tubing from your favorite auto parts store.

 

post-16716-0-68154300-1403796648_thumb.j

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Replaced the oil cap and I got noticeable performance improvement.  The faults are still showing up after I scan for errors (P1128, P1130, P1126, P1133),

Do I need to clear the codes and let it run and see if they come back?

 

Also, I get some smoke when I start the car when the car is sitting for a couple of days...otherwise, none or very little. Can it still be the AOS?

 

T

Yes you will have to clear the codes, they will not clear automatically. If the codes come back AOS is suspect. When you remove the oil fill cap (warm engine) does the oil fill tube sound like a shop vac? Did the RPMs drop (look a tach)?

 

With engine idle and oil cap on, idle revs from 690 to 730 or so.  With oil cap removed while engine idles, revs fluctuate from 640 to 800 or so.

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Replaced the oil cap and I got noticeable performance improvement.  The faults are still showing up after I scan for errors (P1128, P1130, P1126, P1133),

Do I need to clear the codes and let it run and see if they come back?

 

Also, I get some smoke when I start the car when the car is sitting for a couple of days...otherwise, none or very little. Can it still be the AOS?

 

T

Yes you will have to clear the codes, they will not clear automatically. If the codes come back AOS is suspect. When you remove the oil fill cap (warm engine) does the oil fill tube sound like a shop vac? Did the RPMs drop (look a tach)?

 

With engine idle and oil cap on, idle revs from 690 to 730 or so.  With oil cap removed while engine idles, revs fluctuate from 640 to 800 or so.

 

AOS is probably OK... Clear the codes and see if they come back.

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Replaced the oil cap, cleared the codes, and after 60 miles got P1126 and P1133 with pending P1130.  I noticed that when the car is cold, the revs fluctuate to the point that if I put it in gear (tiptronic) and hold the break to the point where the car slightly is able to move, the car moves in a non-uniform fashion like is moving forward and stops, moving forward and stops.  This happens only when the car is cold.

 

I took some pictures with some visible oil stains...is this normal and what to expect?

 

 

 
 
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