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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old October 19th, 2018, 23:05   #1
horn
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Default Mass Air Flow Vag Com Test (confusion) and IQ Deviation

Have a check engine light on for the MAF (P0102 - signal too low)

I let it warm up and revved it to 5100 rpms while plugged in. One weird thing though was the first time I did it, the car went to a little over 3000rpm and kicked it back down. Then I did it again and it went to 5100. Same thing happened when I had it disconnected.

While connected, I did multiple 2nd gear, 3rd gear, and some 4th gear 2k to 4k runs. VCDS showed that the specified reached 850 (peak) and the Actual stayed at 550. Yep, you read that right, the actual didn't change and stayed at 550. I disconnected it and had the same results. To my knowledge that should have went around 850 or 1k. Just not sure if the problem could be anything else. The car has been doggy for a little while, but some of that had to do with IQ being too high.

Another strange thing, I ran test for group 13....IQ Deviation. Cylinder one was .49 while 2,3,4 where -.31,-.14,-.05......so cylinder 1 was well into positive while the other 3 were negative. I don't know much about these tests.

So what do you guys think? Thanks in Advance
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Old October 20th, 2018, 15:25   #2
mk3
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A common problem with these engines is that the intake manifolds become clogged over time. Have you cleaned the intake recently? I've done this to my car twice during the 200k miles I have owned it - one time it was pretty bad and was limiting the engine performance.
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Old October 20th, 2018, 16:04   #3
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Have not. It has about 326k miles on it now. I've had it for 50k. No idea if it has been cleaned, but I know the turbo has been removed and rebuilt before I purchased (have paperwork).

I'm just not sure how the computer reads those numbers.
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Old October 20th, 2018, 18:02   #4
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Quote:
Originally Posted by horn View Post
Have not. It has about 326k miles on it now. I've had it for 50k. No idea if it has been cleaned
You can remove the ASV and look inside the manifold.
You will need an o-ring and a gasket for the EGR tube.
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Old October 20th, 2018, 23:51   #5
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Sweet baby jesus that thing had a lot of carbon build up. Been working on it tonight. Took the intake off and the big pipe right behind/underneath. I'll get some pics.
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Old October 23rd, 2018, 00:45   #6
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Well, I was hoping I could just post the pics off my phone, but can't. The Egr was about 80% clogged, if not more. Not exaggerating either. The intake had a lot too and I think it was near clogged at the 90 degree bend.

All cleaned and definitely has more power. Not much of a shock there. The MAF light is still on, so I'm going to swap that out. Looking at EGR delete or disconnection too.
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Old October 23rd, 2018, 19:27   #7
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All cleaned and definitely has more power. Not much of a shock there. The MAF light is still on, so I'm going to swap that out. Looking at EGR delete or disconnection too.
Did you clear the code to see if it comes back?
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Old October 24th, 2018, 01:20   #8
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The reason that the MAF shows 550 is that is the default value that the ECM will substitute if it thinks that the signal is no good. These cars had problems with MAFs in the early years and are very sensitive to changes with them. You can try MAF sensor cleaner, and make sure that there are no open paths to the turbocharger after the MAF except the crankcase vent. At the end of the day you may end up putting a MAF in it. Do not to the EGR without proper ECM tuning, or you will end up with a CEL.

Did you have your foot on the brake when you attempted to rev while stopped? The ECM will not allow brake and gas to be depressed at the same time- if they are, RPM is generally limited to around 1500.

Deviation looks fine on the injectors.
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Old November 16th, 2018, 11:39   #9
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Sorry all.

I replaced the MAF with a cheapo ebay one and the car runs great now! Almost like a different car. Ive had the car for 2 years and it probably runs better now than ever.

I did end up deleting the egr cooler and all that with a $20 kit from ebay. It had 2 block off plates. I don't care about the check engine light.
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