View Full Version : P1128

07-18-2009, 12:57 PM
Hi all,

The code P1128: Fuel Trim too Lean (Long Term) has been a recurring problem of mine. I cleaned the MAF and it went away for a while. Now my problem is that I'm getting misfires under harder acceleration (and up some hills) and she doesn't pull as hard as she used to.

I logged in VAG (I forget which group, but it's the one that tells you if you're having misfires and on which cylinder) and was indeed getting misfires. Most of them were on cylinder 2 but there were a couple on each of the others. That leads me to believe that it's not coilpacks.

Currently, I'm running some injector cleaner through it, but what are your impressions? Am I wrong and it is coilpacks? Or is it a bad injector... bad fuel filter... bad plugs?? Help me out.

07-18-2009, 01:10 PM
Running lean would be more around a bad primary 02 sensor or MAF. Swap ignition coil from cylinder 2 to cylinder 3, and see if the misfire moves to the 3rd cylinder.

And a code for having random misfires does not mean that you have misfires in random cylinders. Just that you have random misfires. If VAG Com says that you have misfires in cylinder 2, it is because you were/are having random misfires in cylinder 2.

Also, be sure that you have a full tank of gas when using fuel injector cleaner.

07-18-2009, 02:00 PM
I didn't get any codes for misfires though. So you think it's two separate issues? i was thinking that it could be the fuel filter. I've only had this car for 3 months or so and I doubt that the fuel filter was ever changed so I jumped to that conclusion.

07-18-2009, 03:21 PM
the fuel filter is supposedly a lifetime filter. it does get some restriction in it after 100k miles and its worth changing, however ive never seen a fuel filter clogged enough to actually cause you to run lean.

do you have a boost gauge? are you getting good boost and vacuum? you sure theres no leaks?

07-18-2009, 03:36 PM
I highly doubt it is the fuel filter. As previously stated, running lean usually has to do with a bad primary 02 sensor or bad MAF. I would look into those first. I am no expert at logging, but I would log the MAF (block 003 going WOT in either 2nd or 3rd gear to redline).

And as ghost6303 asked, do you have a boost gauge? A big enough leak will have you running lean, so it would be good to know what hg/in you are getting at idle and cruising with foot off throttle. Also, how much boost you are recieving?

Is your vehicle stock? And if it is not, did you do the required upgrades to make your vehicle run properly?

07-18-2009, 09:28 PM
100% stock so far. I figured I'd get the maintenance and upkeep out of the way first. I don't have a boost guage yet but should have one soon. I don't have any major vac leaks as far as I can tell.

07-19-2009, 07:04 AM
You would need to perform a boost leak test to confirm that. This is the technique I use (http://www.a4mods.com/index.php?page=webcontent/pages/boostleak.html). Visual inspections are always good, but you would really need to do a boost leak test to determine the leak. Either way, you would need a massive obvious leak (audible) to be running that lean and cause misfires.

But, I still say you either need to replace your primary 02 sensor or MAF. I am going with MAF, as it was causing issues for you before. And they are known for going bad.Click this link (http://wiki.ross-tech.com/index.php/17536/P1128/004392).

07-19-2009, 08:02 AM
Thanks very much for your help Seerlah.

07-19-2009, 08:04 AM
No problem. Also, you may want to replace your air filter if it is dirty. As that would be the main reason your MAF went faulty. But if your filter is still clean, disregard that suggestion. And if you are going to replace your MAF (which I would do after log confirmation), make sure to use only an OEM Bosch unit.

07-19-2009, 08:27 AM
if your car has over 100k-120k miles on the original MAF you might as well do it anyway. you will gain some fuel efficiency as well. i gained about 5mpg by replacing mine and figure it will pay for itself in gas savings within 9k-10k miles. i got mine from germanautoparts.com, they were the cheapest at $190 shipped for a new bosch unit. they are in NY and i got it within 24 hours and im in CT. you are in NY so you should get it by next day as well.