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Old 01-24-2021, 12:44 PM   #1
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CEL P1128 P1130 persistent

hello...i'll try to keep this concise; 2001 Boxster at purchase 105Kmiles; CEL P1128 P1130; replaced MAF Sensor twice as CEL with same codes; occurs mostly while idling at intersections; replaced O2 sensor, fuel pump; oil separator, cleaned throttle body housing; spark plugs; gas filler cap; same result; **at every fillup the vehicle initially fails to fire, only turns over with no ignition; after several attempts it fires but runs very rough and stalls until after driving 1/2 mile or so and then OK, however, CEL continues to come on after clearing

Any thoughts, suggestions?

thanks

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Old 01-25-2021, 01:43 PM   #2
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hello...i'll try to keep this concise; 2001 Boxster at purchase 105Kmiles; CEL P1128 P1130; replaced MAF Sensor twice as CEL with same codes; occurs mostly while idling at intersections; replaced O2 sensor, fuel pump; oil separator, cleaned throttle body housing; spark plugs; gas filler cap; same result; **at every fillup the vehicle initially fails to fire, only turns over with no ignition; after several attempts it fires but runs very rough and stalls until after driving 1/2 mile or so and then OK, however, CEL continues to come on after clearing

Any thoughts, suggestions?

thanks
Those codes are for telling you that the fuel system has reached the rich mixture threshold for both banks. In other words it is adding all the fuel it can.
The system adds fuel in response to lean conditions.
So you most likely have a vacuum leak.
Hard starting when warm and lumpy or rough idle are also indications of a vacuum leak.
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Old 01-25-2021, 01:58 PM   #3
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Those codes are for telling you that the fuel system has reached the rich mixture threshold for both banks. In other words it is adding all the fuel it can.
The system adds fuel in response to lean conditions.
So you most likely have a vacuum leak.
Hard starting when warm and lumpy or rough idle are also indications of a vacuum leak.
hello, yes and i have previously had the vacuum tested with a smoke test; some repairs were necessary and after those the smoke test did not produce any leaks
the mechanic i have has over 20 years with porsche and even he is stumped
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Old 01-25-2021, 03:12 PM   #4
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hello, yes and i have previously had the vacuum tested with a smoke test; some repairs were necessary and after those the smoke test did not produce any leaks
the mechanic i have has over 20 years with porsche and even he is stumped
one would have to look at some data like O2 sensor waveform and fuel trim waveform under various conditions. perhaps something like O2 sensor signal bias is an issue.
Meaning if your O2sensor signals are biased lean then the system will try to adjust by adding fuel. But it is unlikely that both sensors have the same issue and only in a certain RPM range.

The hard starting situation at fill up followed by poor running-- does that only happen at fill up?
How does the car run off idle? Mid range RPM and upper range RPM?
Is the car stock? Stock exhaust? Stock air filter?

Oops sorry just reread your original post and see that O2 sensor was replaced.

Last edited by blue62; 01-25-2021 at 04:59 PM.
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Old 01-25-2021, 03:43 PM   #5
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What brand MAF? Bought a Bremi that lasted 2k mi. Replaced it with Bosch 5k mi. ago, no issues.
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Old 01-25-2021, 08:23 PM   #6
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one would have to look at some data like O2 sensor waveform and fuel trim waveform under various conditions. perhaps something like O2 sensor signal bias is an issue.
Meaning if your O2sensor signals are biased lean then the system will try to adjust by adding fuel. But it is unlikely that both sensors have the same issue and only in a certain RPM range.

The hard starting situation at fill up followed by poor running-- does that only happen at fill up?
How does the car run off idle? Mid range RPM and upper range RPM?
Is the car stock? Stock exhaust? Stock air filter?

Oops sorry just reread your original post and see that O2 sensor was replaced.
thanks for the input, i am certain it was bosch on the maf; i am getting ready to just replace the MAF again along with all O2 sensors to see what changes, if anything; the idling is intermittent but usually acts up after being off when at running temp and if not moving out of gear it will sometimes just stall, forcing a restart;
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Old 01-25-2021, 08:27 PM   #7
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thanks for the input, i am certain it was bosch on the maf; i am getting ready to just replace the MAF again along with all O2 sensors to see what changes, if anything; the idling is intermittent but usually acts up after being off when at running temp and if not moving out of gear it will sometimes just stall, forcing a restart;
and yes, all stock equipment......i just had a minor service, fuel filter and air filter with no change on the symptoms........higher rpm is fine, only the stopped and/or idling has issues plus only the refuel problem but that is only when refueling when it fails to fire up and causes several restarts after cutting out.....once i force it thru that with 1/4 to 1/2 mile of driving that issue goes away
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Old 01-25-2021, 09:01 PM   #8
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For the re-start trouble, look into "Evap Purge Valve". It's a valve under the left side intake. Here's an article on the basics (not Porsche, but similar): https://www.samarins.com/glossary/purge-valve.html
It may not be the cause of the P1128/1130, but it is likely still part of the problem.

Here's one discussion here: http://986forum.com/forums/performance-technical-chat/50264-success-finally-fixed-hard-start-while-hot-fueling-issues.html
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Old 01-25-2021, 09:20 PM   #9
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For the re-start trouble, look into "Evap Purge Valve". It's a valve under the left side intake. Here's an article on the basics (not Porsche, but similar): https://www.samarins.com/glossary/purge-valve.html
It may not be the cause of the P1128/1130, but it is likely still part of the problem.

Here's one discussion here: http://986forum.com/forums/performance-technical-chat/50264-success-finally-fixed-hard-start-while-hot-fueling-issues.html
thanks!.....that "hart start" post sounds like the cure......much appreciated!
i'll update once i've tried that
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Old 01-25-2021, 09:37 PM   #10
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Have you changed the oil cap? Mine had the same codes and I replaced everything you did. O2, MAF, AOS, plugs, etc. I changed the fuel and oil caps to new and it seemed to fix the problem. Looking at my oil cap and fuel cap, there was small cracks on the o rings. My codes seemed to always come up during traffic and city street conditions. Less on highway going at the speed limit or a little above.
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Old 01-25-2021, 09:45 PM   #11
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Have you changed the oil cap? Mine had the same codes and I replaced everything you did. O2, MAF, AOS, plugs, etc. I changed the fuel and oil caps to new and it seemed to fix the problem. Looking at my oil cap and fuel cap, there was small cracks on the o rings. My codes seemed to always come up during traffic and city street conditions. Less on highway going at the speed limit or a little above.
i had done that but with local auto parts store parts; i just ordered factory replacements today as part of the ongoing troubleshooting......thanks!
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Old 01-26-2021, 05:10 AM   #12
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With the problems at refill that points to the EVAP system. I would check that system out before replacing anymore sensors or other parts.
There are parts of the EVAP system that are under vacuum while running.
Issues with certain EVAP valves will not show up with a smoke test. So you can have a vacuum leak in the EVAP system that is not detected by a smoke test.
A vacuum leak in the EVAP system can cause your codes and all your other issues.
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Old 01-26-2021, 06:55 AM   #13
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thanks for the input, i am certain it was bosch on the maf; i am getting ready to just replace the MAF again along with all O2 sensors to see what changes, if anything; the idling is intermittent but usually acts up after being off when at running temp and if not moving out of gear it will sometimes just stall, forcing a restart;
To just replace parts (sensors) is not a good diagnostic procedure. Testing sensor output and function is the proper way to go.
You have already replaced the mentioned sensors with no change so it is not a problem with said sensors. The problem is as the code says. A lean condition in RPM range 2
almost certainly a vacuum leak. I see you have smoke tested for vacuum leaks and corrected some. But here is the thing a smoke test is not 100 % foolproof. You can still have a vacuum leak. Most likely in the EVAP system as your issues at refill indicate.

Your running issues are at low RPM or idle and you say it runs ok at mid and higher rpm
most likely the more RPM you give it the better it runs. Those are classic indicators of a vacuum leak. It is not a fuel delivery problem. If it was your low RPM running issues would get worse as you tried to give it RPM. Fuel delivery demand increases with engine load and RPM. It runs fine at mid to higher RPM so it is not a fuel delivery problem.

I would look at the EVAP system. There are several components that are under vacuum in that system.
Your issues at refueling are pointing right at this system.
Hope this helps some and give you a better direction to go.
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Old 06-22-2021, 09:30 AM   #14
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I just bought a 2000 Porsche Boxster S from a friend and mechanic. It has 68k miles on it and has been well cared for. A week ago I got a CEL, codes P1128 and P1130. Previous owner tells me the MAF sensor was replaced recently. Twice in the past few weeks, the car stalled while slowing down (clutch in, engine speed went to idle, then stalled). What is the first thing to check? From reading these threads, I hear discussion of fuel cap (checked), oil cap, oil fill tube, O2 sensors (there are 4, so quite pricey). Where should I start? Should I stop driving it until it's repaired?? Help appreciated.
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Old 06-22-2021, 10:43 AM   #15
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I just bought a 2000 Porsche Boxster S from a friend and mechanic. It has 68k miles on it and has been well cared for. A week ago I got a CEL, codes P1128 and P1130. Previous owner tells me the MAF sensor was replaced recently. Twice in the past few weeks, the car stalled while slowing down (clutch in, engine speed went to idle, then stalled). What is the first thing to check? From reading these threads, I hear discussion of fuel cap (checked), oil cap, oil fill tube, O2 sensors (there are 4, so quite pricey). Where should I start? Should I stop driving it until it's repaired?? Help appreciated.
So those two codes are tell you that the system has reached the enrichment limit.
So the air fuel mix is to lean.
Most likely cause is an intake vacuum leak.
There can be other causes but start with the simplest things first.

The first thing you want to do is buy a vacuum gauge and do a proper vacuum test.
A vacuum gauge costs around $20.00
hook the gauge to an intake source on the intake. or the brake booster vacuum hose. At idle gauge should read 18-21 inches of mercury with a steady needle.
Or
Google automotive vacuum testing or go to youtube so you know what your looking for and how to do a vacuum test properly.

Let us know what you find.

Driving the car with this issue "could be" damaging to the catalytic converters.
They are very pricey to replace.

Last edited by blue62; 06-22-2021 at 11:26 AM.
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Old 06-22-2021, 11:29 AM   #16
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A week ago I got a CEL, codes P1128 and P1130. Previous owner tells me the MAF sensor was replaced recently.

I had these same codes- a new MAF sensor solved the problem. Make sure that the replaced MAF is the correct part# and a Bosch unit not a cheapo knock-off.

FYI- I had no luck cleaning the bad MAF which had been dealer installed less than 3000 miles before, by the previous owner.

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