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Discussion Starter · #1 ·
Let us solve this problem once and for all. It cannot be that complicated.
I need to get this CEL light off to pass emissions. Car runs great except it feels like the throttle is "floaty" sometimes.


 

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17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean

Potential causes.

Vacuum leak after the MAF.
Bad MAF.
Bad #1 O2 sensor.
Low fuel pressure.
 

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When I had a P1128 it turned out to be the MAF. I tried to clean it first, but it didn't help. Do you know if your vacuum lines have ever been replaced? It's pretty easy and much cheaper than a MAF. There are some posts with pictures of where the lines run, I replaced mine with 3.5mm silicone.

You can monitor the output of the MAF with Vag-com (VCDS). This is the easiest way to tell if it is good or bad.
 

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Tell me more about a VCDS this is a new one for me.

And yes my vac lines are good
do a google search on VCDS, or VAG-COM. best troubleshooting tool there is for VW/Audi and many, many other cars.

I know from experience that unless you have personally replaced all of your vacuum lines, you don't know your vacuum lines are good.
 

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I had the 1128 a few weeks ago. If I cleared the code, it would run fine for about 2 cold starts, then it would only boost 5psi. Shortly after the CEL would light. THrough all this, no idle.drivability issues.

Replacing the MAF fixed this 100%.
 

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I had a steering knuckle in my shed. Really!
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4,159 Posts
Use the VCDS to check to fueling trims--maxed out additive trim points to vac leak; maxed out multiplicative trim points to MAF or fuel.
 
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