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Discussion Starter · #1 ·
Have been spending a lot of time here searching and searching (and a bit of searching) and have found a few threads with similar issues. Have also been blown away by the knowledge out there and the love for the Passat. The best part for a research junkie like myself has been the insight into the minds of the well versed experts out there who can make sense of the subtle and sometimes cryptic hints these cars give to their issues!
I can give the exact opposite. I view into the minds of a keen beginner. So here we are:

Since purchase of my '98 1.8t (AEB) it has shown a slight stumble under light acceleration. This can sometimes be mistaken for a rough road, but it is getting worse. There are several things I can see wrong with the car, some of which may be related, so here is what I have noticed:

Stumble is most obvious when accelerating between 35-45 mph. This is converted roughly from kmh (60-70) but corresponds to 1600-1800 revs. By 2000 revs it is no longer noticeable.

It is worse with lower octane fuel. We measure octane ratings differently here in New Zealand. The cheap stuff is 91, premium 95 and some stations (including, unfortunately, everyone's favorite BP) sell 98. Shell V-Power is 95, gives a more noticeable stumble than BP's 98 but perversely more power and better fuel economy. I think this is the first red herring ;)

Dealership have had this a few times and apparently can't do anything until it gets worse (and presumably throws a code.) Bit surprised they didn't spot the disintegrating vac line to the DV. You could see the rubber through the braiding and it didn't look good.

There is an oil leak dripping onto the cat, which I take to be the valve cover. Makes me think PCV system. There is a decent amount of oil on the other side of the engine too.

This is what I have done to the car since purchase, about 3 months ago:

Trans flush
2 oil and filter changes at the dealership with 502 spec oil
New spark plugs (also x2) the local indie used the wrong spec and the dealer replaced with turbo suitable
New air filter
New fuel filter
New coolant temp sensor
New thermostat
Irrelevant but annoying - 2 door locks
2 scans at the dealership, no codes
Cleaned the throttle body. Did this without removing. Very slight and very fine dark deposits, more like dust, that wiped off easily with carb cleaner.
Throttle body alignment at dealership
Replaced the 2 easy vac lines with 3mm silicone, no need for clamps. Still holding firm. Used opaque silicone. No signs of oil or anything in them. Really don't enjoy removing one use clamps! Particularly from DV. Mental note to get some bigger cutters. Other vac lines I can see look fine, although until I get a manual I am not sure where they all are, particularly if there are more braided ones than those going from the IM to the DV and FPR.
Have removed air intake temp sensor and cleaned with alcohol and maf cleaner. Seems to be coated in a amber varnish that neither cleaner was able to remove. MAF cleaner was used with a pipe cleaner. Will try with carb cleaner but don't want to mess up the plastic. Will replace if carb cleaner doesn't do it.

And finally the limitations:
Knowledge (any help appreciated:))
Basic tools
No VAG com. Am contacting a local VW club to see if anyone has one. Dealership apparently keeps a printout and are digging them out so I can have a copy. Will post results when I get them.
Manual on the way (Haynes)

Purchase price = NZD $6000
Above maintenance around NZD $3500-$4000 and counting
Happiness = low and getting lower
Car is a genuine pleasure to drive when not in the above mentioned rev range,I can understand the love for the car, but cannot justify the cost. My conscience will not let me sell this car on until the stumble is fixed.

Please help!
 

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at some point some mechanic broke mt PCV system and decided to tape it back up. I had the same acceleration issues, So their is a good chance thats it, also a fairly inexpensive repair and not a bad thing to get replaced. :salute:

Also dont change your octane its bad on the car, try to always buy atleast 91 premium (thats what I put in my car in US), Ive put the cheap stuff in because I didnt have enough to get home if I paid the extra $1 (No card, $5 cash lol) and it reaked havoc on my car until I ran cleaner and about 2 tanks of 91 later, im sorry passat....
 

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Discussion Starter · #3 ·
at some point some mechanic broke mt PCV system and decided to tape it back up. I had the same acceleration issues, So their is a good chance thats it, also a fairly inexpensive repair and not a bad thing to get replaced. :salute:
QUOTE]

It's great to find someone who has had the same issue, Thanks!
I will need to wait for the manual before tackling the PCV system. I cannot find a definitive post to cover this. Thanks again!
 

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at some point some mechanic broke mt PCV system and decided to tape it back up. I had the same acceleration issues, So their is a good chance thats it, also a fairly inexpensive repair and not a bad thing to get replaced. :salute:
QUOTE]

It's great to find someone who has had the same issue, Thanks!
I will need to wait for the manual before tackling the PCV system. I cannot find a definitive post to cover this. Thanks again!
Same thing with mine since I bought it new. It doesn't really bother me but a friend of mine in our local VW club pointed it out while we were on a road trip. Says his mother's Passat does it too. Her 1998 is an AEB engine, my 2001 is an AUG. Description is very good, it feels like you are driving on a slightly bumpy road while at those speeds. I just figured that it is related to the forced induction. My old Saab turbos don't do this but they have simpler control systems and emissions so I figured that lumpy power delivery on the newer cars is the norm. AEB is throttle cable vs. AUG's DBW so it can't be attributed to the DBW. Same with the variable valve timing. AUG has it, AEB doesn't.
:wrench:
 

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Discussion Starter · #5 ·
I'd be pretty surprised if that is as good as it gets, just because it seems to be getting worse so I figure it can get better. But your's has done this since new? :icon_eek:
I wouldn't be very happy about that....
 

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Discussion Starter · #7 ·
Thanks PZ, it's good reading! So if the dealer ever coughs up the diagnostic printout, a good place to start would be misfire count?
I am not getting the bbbbbbbbbt sound (or any other when the stumble is happening) but doesn't rule it out I guess. Others in that thread were having similar issues with the air filter screen blocked. I am hoping that the dealer would have cleared this when they did the air filter....although I was hoping they would have spotted the bad vac lines too ;)
 

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I will be interested in hearing how you solve this. I just picked up my passat from the dealer and naturally noticed a couple things that I didn't notice in the previous three test drives. The stutter was one of them. I'll definitely be replacing the pvc valves first.
 

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Discussion Starter · #9 ·
No worries Branson, I'll be keeping this thread going until the stumble is banished from my rev range.

This post is both a test of whether I have sussed out how to post photo's, and to ask the question - "Any chance this looks like a PCV system in distress???"



 

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Yes, it looks like that PCV has issues. The plastic elbow might be cracked or the seal is on the block side. It looks like the rubber T may have been replaced before as it has screw clamps on it instead of the 1 time use clamps. Should make it a bit easier to remove it.
 

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Discussion Starter · #11 ·
Good stuff, thanks PZ :thumbup:
It looks like we are getting to the bottom of this, and I now have a few things to work on.
The carb cleaner didn't seem to remove the varnish on the AIT but the car is better today. It sometimes does that though, so will not get hopes up yet.
From here:
1. Replace AIT sensor
2. Replace whatever needs to be replaced to get that PCV back into shape.
In that order. At least if I do them separately we will know what was causing the stumble. If neither of those works, coil packs are the next thing to check, but I'll see what happens after 1&2 first.
 

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I do 1-2 a year and it along with the coolant flange is my least favorite job. I use a set of long screwdrivers for most of the work, but then have to remove the coolant tank and jam my arms in there to finish.
 

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I'd be pretty surprised if that is as good as it gets, just because it seems to be getting worse so I figure it can get better. But your's has done this since new? :icon_eek:
I wouldn't be very happy about that....
Doesn't bother me much and doesn't bother my friend much either. He bought his used, with something like 40k, and it has been doing this all the way to now. I think they are at 140k.

I doubt that it is coil packs. I can look at the misfire count on mine with VAG COM and see anyway, but mine has done this through at least 2-3 rounds of dealer-replaced coil pack versions, and my friend's AEB has Hitachi coil packs which are different than the ones on my car.

Your description is spot-on so I feel like we are talking about the same phenomenon at least. Same feel, same speeds, light to medium throttle, and it feels like little bumps in the road.

:wrench:
 

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One more thought... I had some 87 octane in the car when we first noticed this and you say that it is worse for you with lower octane. I wonder if what we are feeling is the knock sensor kicking in and dialing the timing back a bit because of the lower octane fuel? Then again, you'd expect that more under full throttle.

Maybe something funny with the fuel and/or timing maps at those rpms and loads?
:crazy:
 

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My 2000 with an ATW started doing this a bit a year ago, and it was indeed the very begining of a coil pack failure. No check engine for it btw.
Probably a different issue. I've never had a single problem with coil packs but I've had them replaced whenever I've received notices from VW. The car has done this through all coil packs but I've never paid much attention to it because it is so minor. If it happened at sustained highway speeds I'd be more concerned, but it's only doing it around 30-40 mph at light to medium throttle.
:wrench:
 

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Discussion Starter · #18 ·
One more thought... I had some 87 octane in the car when we first noticed this and you say that it is worse for you with lower octane. I wonder if what we are feeling is the knock sensor kicking in and dialing the timing back a bit because of the lower octane fuel? Then again, you'd expect that more under full throttle.

Maybe something funny with the fuel and/or timing maps at those rpms and loads?
:crazy:
I had thought about the knock sensor, but imagine that this would only come into play if using an octane so low that the timing cannot be changed enough to fix it. With the timing pulled for slightly lower octane fuel surely the only effect would be less power? At the highest octane fuel available, it shouldn't be a factor.....unless it is the knock sensor itself??? Oh dear!
I am pretty convinced that the PCV is at fault here, particularly as it is clear a PCV issue can cause this behavior and I have oil where oil should not be! But am secretly hoping a new AIT sensor will do the job. Unfortunately the part has to come from Singapore, so it will be 4-5 days before I can even try it. :thumbdown

On a bad day I can feel this while cruising at 100km/h, but you need a pretty smooth road to notice it and that is not very common where I drive :)
 

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Discussion Starter · #20 ·
My car's stumble went away after changing the timing belt. I'm glad I changed the belt the second day I owned the car. The tensioner wasn't applying any tension at all. I was just flapping. I'm lucky I made it home.
So are you thinking the belt had slipped a notch? I remember a thread with similar issues where this was the culprit....
 
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