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Old 01-24-2011, 03:10 PM   #1 (permalink)
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Jetta - '98 Volkswagen Jetta GLS
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Sudden 50% INCREASE in consumption

You read right. I have lost just over 10mpg on my normal trips.

I have been battling P1128 (long term trim too lean) issues for about a month. I could clear the code and get an extremely rough idle for awhile, until the short term trim maxed out at 25%. Then it would run okay. 10 miles later, the long term trim would set at 23% and the car ran wonderfully. City trips around 34, idle at 0.25 gph.

Last night, I popped the hood and found that I had either bumped or never reconnected the PCV valve to the intake. I reconnected that and took it for a drive. Started right up, smooth idle, smooth acceleration. Then I took a look at my UltraGauge. Short term trim is hovering a few percent around zero (good). Long term eventually has set itself around 3%. Idle gph is now 0.38 and my city trips are at 24. Even my 60 mile cruise on the highway got me 26 instead of 35.

Has the ECU just not relearned its stuff after driving with an intake leak for so long? Any ideas on what could have gone wrong?

98 Jetta 2.0L. I currently do not have any codes.

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Old 01-24-2011, 03:18 PM   #2 (permalink)
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Amazing story. I have disconnected the battery for 20 minutes to reset the computer to factory defaults. Maybe a faster way to force the ECU to learn.
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Old 01-24-2011, 03:29 PM   #3 (permalink)
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Yeah sorry about the saga, but man is this aggravating. I pulled a plug out to look at it, but that's the only thing I can think of that changed.
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Old 01-24-2011, 06:58 PM   #4 (permalink)
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You need to reset the ECU , as far as ECU goes you fixed a issue it was having (lean condition-P1128 code) .

That should clear it up .

Ed
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Old 01-24-2011, 07:03 PM   #5 (permalink)
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Thanks, I did. Strangely, I got 31mpg on that short tank (29 miles). The UG's fuel calibration was reading 1.3x, and after that fill, I recalibrated it.

I have a trip into Chicago tonight (175 miles). We'll see what happens.
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Old 01-24-2011, 10:02 PM   #6 (permalink)
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watch out it is frosty out there
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Old 01-25-2011, 05:07 AM   #7 (permalink)
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I hit 200 miles and the needle is on the halfway mark, which historically has indicated a ballpark 34-35mpg. I'll fill tomorrow. Son of a gun...I think the calibration jumped somehow.
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Old 01-25-2011, 02:40 PM   #8 (permalink)
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With the computer confused before, it probably screwed up the calibration.
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Old 01-27-2011, 11:16 AM   #9 (permalink)
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Solved. It was indeed the fuel calibration. I filled last night and hit 36 actual mpg; UG said 37.2, but historically, it has read a bit high. All good now!
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Old 01-27-2011, 11:57 AM   #10 (permalink)
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Sounds good!

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