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Fuel Trims?

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I am working on an intermittent CEL.

two codes cam up this winter 1130 (alone) and later 0103 (alone)

Both times I cleaned the MAF.

I am now keeping closer tabs.

Today I downloaded fuel trims...

LT 1 = -15.6

LT2 = - 16.4

Does this shed light on the sbject for anyone?

your MAF is fried. these trims indicate that your MAF is setting the fuel mixture quite rich and the O2 sensors are forced to lean out the mixture.

the reason the 1130 is thrown is this: your LT1/2 trims are lean because the MAF is sending rich ABOVE IDLE but normal at idle. the ecu compensates with negative trims. when you slow to idle, though, the MAF signal is okay (not rich), so the lean fuel trims cause a short term lean condition that the computer can't compenate for (it's reached the enrichment limit and the car is STILL running lean). basically, your short term trims are near +25% at the instant this occurs.

the 0103 code tells us that the MAF is sending a voltage that's higher than the max it's supposed to send. this confirms the fried MAF (although technically it COULD be a short, i promise it is not).

Edited by insite
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  • Admin

Uh... the MAF reads air flow and intake air temperature - period. The O2 sensors read NOx, CO, and HC before and after the cats - period. Both report their readings constantly to the DME - the DME then adjusts the richness of the mixture (via fuel injectors) to adjust the air/fuel mixture for the proper burn. When the mixture can not be adjusted properly (with the threshold range of operation) the DME signals a fault code.

What bother me is that he only has the P1130 Oxygen Sensing Adaptation Area 2 (Cylinders 4 - 6) - Rich Threshold - or one side of the engine. Seems to me that you would likely get a P1128 (Oxygen Sensing Adaptation Area 2 (Cylinders 1 . 3) - Rich Threshold) also if it were an MAF problem.

Are you sure you obly have a P1130 and not a P1128 also?

A P103 is pretty unusual - I would check the connector to the MAF and make sure the wires and pins are good condition. All indications do point to a bad MAF or MAF connector.

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Thanks for the input.

Called The tech at Farnbacher Loles. He just asked one question, what is the mileage? told him 30,000. He said definitely change the MAF they just don't last over 30,000. If that doesn't fix it, then we have to chase the vacuum lines.

Bottom line they fully expect MAF. The other stuff would be "zebras."

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  • 8 months later...
Thanks for the input.

He said definitely change the MAF they just don't last over 30,000.

Yeah right and Boxsters are chick cars...

Sorry I didn't see your post sooner. There are plenty of us driving cars with twice and 3 times the mileage on the original MAF.

That said, MAFs do go bad but, MAFs can be cleaned (I use CRC MAF cleaner) with electronics cleaner.

Replacing the MAF is quick and easy and only $300. In my experience, techs recommend this kind of repair because it's easy money, works 50% of the time and when it doesn't work, it's the beginning of a nice $1000 relationship.

Call it cyncism or call it experience - your choice.

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Good thing I don't trust techs.

I cleaned the MAF with CRC. That didn't clear it up entirely -- no codes but driveability concerns. Took it to the dealer - Turns out the pre-CAT was bad on the passenger side. Replaced F.O.C. under the 10 year warranty.

Since then, no codes and better driveability.

I have also since checked the vacuum lines. If not totally cured, I may swap out the MAF. But that is down the road.

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