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Fuel/Air Mixture to lean

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My check engine light came on recently and the two codes were P1128 and P1130. Is they any way to check the O2 sensors myself or should I go to the dealer? Also could this be a MAF problem? The car is A 2000 boxster. I know they can have this problem.


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There is a TSB for MY97 - MY00 Boxsters that states a P1128 and P1130 codes are potentially caused by an air leak in the oil filler hose. P1128 by itself is usually a faulty oil filler cap seal.

Thanks for the help. I actually replaced the oil filler hose and the light came back on. I may try to clean the MAF. Any idea where it is?



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I'll be replacing the MAF sensor on my '99 tonight. Similar problem except I have codes p1123/p1125 (too rich). When I run with the MAF disconnected the only codes I get are the ones that say the MAF is disconnected, no 1123/1125. And the car actually runs significantly better. I am fortunate to have a buddy that loaned me his OBDII scanner to read the engine codes.

The MAF is really easy to access. It is on the air intake right next to the air filter. You will need a torx #20 or #30 security driver (the kind with a hole in the center) to remove the two screws that hold it in place. A replacement should run you about $250 if you order yourself (my dealer quoted me $600 to replace :huh: ).

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Almost 24 hours now w/no CEL!

It is a really easy part to change. I had until recently never even looked at the engine - but instructs for access are in the owners manual. Car seems to run good w/the new MAF but I still seem to get odd readings from one set of oxygen sensors and I am expecting the CEL to come back soon. I don't know what might affect only one side of the sensors, maybe a vacuum leak who knows.

Bought it from autohausaz - the only real issue was determining if I wanted the one for e-gas or not - there are two MAF sensors out there. Does anyone know if the connectors are different? I hope so - I just replaced mine with the same part that was alredady there (non e-gas). But I bought the car used...

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I also have a 2000 with the same codes (1128 & 1130) and this forum and others suggested it was an air or vacuum leak. I checked everything out and could not find anything. I didn't notice any drop in performance once the check engine light came on (first time). So I bought a OBDII tester on eBay for $45 and cleared the readings and waited to see if the codes would come back. Car runs great, gas mileage is excellent (approx. 24 in city driving) but the readings come back every other month or so. I notice they're more likely to pop up when the car is idling for a long time. So, I just keep clearing them. It's been about a year, and no negative consequences by not replacing or repairing anything. I passed Colorado emissions test. I'm not recommending you do the same....just thought I'd share my experiences with those readings.

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  • 2 weeks later...

There are quite a few post about this related topic and it raises a few questions since I am now seeing P1124, P1126 on a regular basis.

Background: MY97 with 95K miles; I was seeing these two codes (always together) about once every 6-8 weeks. Now done to less than 1 week between appears (daily driver; 58 miles round trip) :drive: . I have never had any other codes appear.

In reading thru the post going back over the last year or so on this topic, it seems many people get these codes (or similar) along with some other code (which tends to be the root cause of their problems). In cases where you get codes from both side of the engine at the side time, you need to have a common connection point which is the failure (MAF??) While it possible one could have an O2 sensor failing on both sides of the engine, but my engineering equipment experiences tells me that simultaneous failures of two parts are very rare.

I have the OEM guide to the OBDII codes and have done all the recommended checks; as paid a mechanic to do the same without finding any issues.

Some open questions:

1. What is the difference between P1124/P1126 and P1128/P1130; they talk about different ranges, but not clear what that is.

2. For the MAF, there are two types depending on whether you have e-Gas. From other readings, its seems e-Gas (also called e-accelerator) is an option and thus shoudl appear in the option code list for the car?

3. Read that O2 sensors are recommended to be repllaced at 100K. Any thoughts or experience on this.

I hate playing "swap-a-part" but seriously considering to change the MAF as I know that other auto manufacturers (e.g. Volvo) have lots of problems with this type of part.

Thanks for your thoughts and replies. :thumbup:

Mike in LA

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  • Admin

1. P1124/P1125 covers lean conditions (that the DME can not adjust for) at idle. P1128/P1130 cover lean conditions at close to full load.

2. Egas is not an option. It began on C4's (but not the C2) in 1999. All Carrera's have had egas since MY00. On the Boxster all 2.5' s do not have egas.

3. O2 sensors will deteriorate with age and either the sensor will stop sensing or the heater will not get the sensor hot enough. If you record your O2 readings using a scan toll you can watch the sensor deteriorate. Most folks just wait until a failing or failed sensor throws a CEL.

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it is very important to know if the P1128 and P1130 is above or below threshold. you cannot properly diagnose these codes without knowing and you usually will not know unless you use a PST2. in most cases with P1128 and P1130 i have found that the MAF sensor signal is faulty causing the DME to pull fuel.

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hello redline.....

do your statement about a faulty MAF also apply to P1124/P1126? Sounds like you have dealt with this problem more than once. any other suggestions to check? I have the Porsche OBD II and done all the things they suggest without success. Also a number of other folks posting with similar/ same problem.


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Here's an update on troubleshooting P1124/P1126 on my MY 97 Boxster with 95K. I happen to have the Porsche OBDII book as well as scan tool.

I found that I was also getting a P0130 (O2 sensor, cylinders 1-3) when I started the car up and let it idle in the garage (door open, of course). The scanner updates every 15 scans. Prior to this I always got a P1124/P1126 together but nothing else, but I always checked after the Check Engine light came on. After readin in the book, I ofund that P0130 is a non-latching coode and will be cleared after some time if the fault is "healed". This code is related to the sensor heating up and functioning correctly in the first 200sec. I use my Boxster as a daily driver and drive about 28 miles (45min) each way so it appears that the fault was clearing itself before I got home. Anyways, I replaced the O2 sensor before the Cat today on cylinders 1-3 and the P0130 (or any other code) did not appear on the garge idleing test. Still needs road testing.

Moral of the story is some codes are non-latching and they can be the ones that indicate the part that truly needs to be replaced. Thus, one needs to check in the garage instead of hooking up the OBD II after the Check Engine light come on and you get back to your house.

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