[BusRider]

2000 Passat 1.8T ATW Automatic (117K miles)

I apologize if this is a re-post of a common problem, but my search queries involving the keywords "struggling, hesitating, power loss" yield common results that don't quite match the problem I am experiencing.

At times that I need extra power/acceleration (i.e. accelerate up a steep hill, passing on the freeway), I will notice that the car will literally struggle to accelerate but eventually reaches the desired speed. The RPM, usually at 3000 and up, will steadily increase, oscillating up and down a predictable range. For example: 3000, 2800, 3100, 2900, 3200, 3000, etc...

I recently replaced the air filter and spark plugs in the car (long overdue) and am planning to replace the fuel filter in the near future (never done on the vehicle). After the filter and plug maintenance, as well as cleaning the MAF sensor, I still experience this problem.

What might cause this to occur? This doesn't sound like limp mode, which is a common diagnosis for the search terms I found. Is a vacuum leak check in order? For completeness, I should note that I am holding the throttle pedal steady.

 

[Jonner]

2000 Passat 1.8T ATW Automatic (117K miles)

At times that I need extra power/acceleration (i.e. accelerate up a steep hill, passing on the freeway), I will notice that the car will literally struggle to accelerate but eventually reaches the desired speed. The RPM, usually at 3000 and up, will steadily increase, oscillating up and down a predictable range. For example: 3000, 2800, 3100, 2900, 3200, 3000, etc...

For completeness, I should note that I am holding the throttle pedal steady.

My first thought would be a transmission issue. I would start looking into bad torque convertor symptoms, low transmission fluid. This is speculation, so I'm not too sure (haven't dealt with a similar problem myself). Although, I would expect to see more fluctuation (higher revs that finally settle into lower revs once a gear stops slipping). If you change your behavior around the shift points (avoid full throttle) and ease into each gear does it help? Does tiptronic see the same result or is it only in "D"?

 

[Tomvw]

A Scan would be a good idea at this point, it might narrow down the possibilities.
I think Autozone does it free, but it only scans the ECU.

A VCDS (VAG-COM) scanner is a very useful tool for diagnosing many types of faults.
VCDS-Lite will scan all your scannable modules and perform some tests and procedures.

You can buy a VAG scan cable for VW/Audi on eBay for about $10.00.
(This connects to the OBDII Port in the car, and to a PC or Laptop Etc.)
And Download the VCDS-Lite, FREE software (or registered software for $99). From:

Ross-Tech: VCDS-Lite
Ross Tech also supply an interface cable with full version of VCDS from $249.00.

Or someone might be willing to scan it for you.
Just enter your zip code and it should give you the closest person and their contact information.

VWVortex.com - Vag-Com Locator searchable map style! Owners pm me your info requested in the thread

 

[JayTheSnork]

it also might be a good idea to check your transmission fluid level.

 

[Tomvw]

First you need to get a VCDS scan of all modules and post the results.
Does the car speed fluctuate with the RPMs, or is the car speed constant while the RPMs are changing ?

 

[BusRider]

If you change your behavior around the shift points (avoid full throttle) and ease into each gear does it help? Does tiptronic see the same result or is it only in "D"?

I did some experimenting on my way to work, albeit limited due to traffic. Here are some notes:

I do not observe the problem when the tiptronic is engaged. I floored the pedal in 5th gear and speed and RPM climbed steadily, well above the 3000 RPM mark. After slowing down to about 60mph, I downshifted to 4th gear, and accelerated again, observing no problems.

I only observed the problem when already in motion, tiptronic disengaged, in gear 3+. If I accelerate from a stopped position, the turbo kicks in, and RPM increases well above 4000 without regression. However, when the pedal is floored, there is a short, faint, wheezing/whistling sound from the left side of the vehicle (audible inside cabin) that coincides with the frequency of the oscillating RPM.

I rarely drive the car this hard, and I usually keep the RPM below between 2000 and 2800 when I am accelerating. I've always eased into the shift points, which is likely the reason I didn't detect this problem sooner.

Does the car speed fluctuate with the RPMs, or is the car speed constant while the RPMs are changing?

I'll pay attention to the speedometer on the drive home today. I've been focusing too much on the tachometer, then realizing I'm at 90mph while testing!

 

[BusRider]

First you need to get a VCDS scan of all modules and post the results.

Unfortunately, a scan didn't produce anything meaningful (auto scan, excluding airbag module) -- see below. The given faults are issues I'm already aware of and am certain have nothing to do with the throttle problem.

As I mentioned earlier, each time the RPMs drop, I can hear a whooshing/air discharge noise from what appears to be the drivers side of the vehicle. Are there any hoses that may contribute to this problem if they were cracked/damaged?

--

Chassis Type: 3B - VW Passat B5
Scan: 01,02,03,08,15,16,17,19,35,36,37,46,55,56,57,58,76

-------------------------------------------------------------------------------
Address 01: Engine
Controller: 4B0 906 018 BH
Component: 1.8L R4/5VT G 0006
Coding: 07551
Shop #: WSC 05311
1 Fault Found:
17977 - Cruise Control Switch (E45): Implausible Signal
P1569 - 35-10 - - - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans
Controller: 8D0 927 156 AN
Component: AG5 01V 1.8l5VT USA 3132
Coding: 00104
Shop #: WSC 05311
No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes
Controller: 8E0 614 111 AH
Component: ABS/ASR 5.3 FRONT D10
Coding: 00021
Shop #: WSC 23322
No fault code found.

-------------------------------------------------------------------------------
Skipping Address 15-Airbags

-------------------------------------------------------------------------------
Address 17: Instruments
Controller: 3B0 920 920 B
Component: B5-KOMBIINSTR. VDO V24
Coding: 07245
Shop #: WSC 05311
No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway
Controller: 6N0 909 901
Component: Gateway K<->CAN 0001
Coding: 00005
Shop #: WSC 05314
No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv.
Controller: 1J0 959 799 AJ
Component: 6W Zentral-SG Komf. 0001
Coding: 04096
Shop #: WSC 05311
4 Faults Found:
00943 - Heated Exterior Mirror: Driver Side (Z4)
35-00 - -
01358 - Internal Central Locking Switch: Driver Side (E150)
27-10 - Implausible Signal - Intermittent
00915 - Window Regulator Switch: Rear Right: Driver (E55)
27-10 - Implausible Signal - Intermittent
00944 - Heated Exterior Mirror: Passenger Side (Z5)
35-00 - -

-------------------------------------------------------------------------------
Address 56: Radio
Controller: 1J0 035 180 B
Component: Radio DE2 0004
Coding: 04043
Shop #: WSC 23322
1 Fault Found:
65535 - Internal Control Module Memory Error
00-00 - -

End --------------------------------------------------------------------------------------------------

 

[Tomvw]

Does the car speed fluctuate with the RPMs, or is the car speed constant while the RPMs are changing ?

You haven't answered this question yet.

You are right, the DTCs don't help with this situation. I don't believe there is a problem with the transmission, it should have thrown codes if there was.
It looks like the turbo system or SAI system, do a search on N75, I don't know much about these systems, hopefully someone
who does will chime in.

 

[BusRider]

Does the car speed fluctuate with the RPMs, or is the car speed constant while the RPMs are changing ?

Yes, it does. When the RPM drops, my foot is still giving throttle, but I can feel the car slow its acceleration -- my torso moves forward when the car slows its motion and I can hear the engine relax as well. The speed continues to increase, but a sharp drop is not immediately noticeable on the speedometer as the change in RPM is fairly small and acceleration varies for a short period of time.

Not sure why I didn't report this, probably because I was focused too much on the speedometer and not crashing into something on the freeway.

 

[GSO_Passater]

Check the L hose on the intake for a crack typically near the elbow. This is a hose that goes from just behind the throttlebody to the bottom of the suction pump. It sounds like this hose has a crack and could be the noise that you hear. If that is the case, then check at the Turbo bypass valve to see if it holds a vacuum.

 

[midnightmekanik]

As others, I think it's a trans issue, or TCM issue. It sounds too much like the torque converter going in and out of lock. With a fluctuation of only 2-300 rpm, lockup seems to be plausible.

Check your trans fluid, if it's really dirty, have it replaced and check the old fluid for particles. I don't know if you have owned this since new, but I wouldn't recommend a trans flush. Just change the fluid. A flush may send it to an early grave if it indeed has trans issues.

 

[BusRider]

Thanks for all the suggestions!

I'm planning to inspect the transmission valve body in the future for an unrelated repair project, so I can inspect the fluid levels then. I changed the fluid about 1 year ago by the book, and didn't notice this problem then. The fluid was black (10+ years old) and there were no large particles sticking to the pan magnets. It could be that the problem has always existed but went undetected since I rarely push the vehicle this hard.

Just to understand the lockup problem a bit better, if this were the case, would it cause the gear to slip? And if so, wouldn't the RPMs surge since the car is accelerating -- that is, is a slip equivalent to being in neutral?

 

[curtie94]

How about a misfire?

A tranny slipping and misfires are a similar feeling

 

[Tomvw]

The reason for this question was to further eliminate transmission slip.

Does the car speed fluctuate with the RPMs, or is the car speed constant while the RPMs are changing ?

And it has.

Also, if there was trans slip, it should be reported by the TCM.
Do as suggested by GSO_Passater.


The scan codes you have posted, appear to have been read soon after clearing, and therefore give little if any useful information.
With the symptoms you have been posting, I would expeect to see some relevant codes. If you keep clearing codes, you are never likely to find intermittent faults.
Disconnecting the battery clears many codes & settings.
Drive for while, several normal drive cycles, do not clear codes or disconnect battery before or after reading codes.
Scan and post engine fault codes, some live data would be good as well.

 

[BusRider]

Check the L hose on the intake for a crack typically near the elbow. This is a hose that goes from just behind the throttlebody to the bottom of the suction pump. It sounds like this hose has a crack and could be the noise that you hear. If that is the case, then check at the Turbo bypass valve to see if it holds a vacuum.

The "L" hose is indeed the source of my problem. Thank your for your insight!

I built a "boost leak tester" with an ABS pipe elbow and connectors, and used my DIY brake bleeder (i.e. garden sprayer) as the pressure vessel. Once the system was pressurized to 1-2psi, the L-hose started hissing exactly at the elbow.

For reference, the L-hose part number is 06B 133 783 BC (replaces 058 133 783L), and the video I used as a basis for doing the boost leak test is here:

 

[GSO_Passater]

I had just gone through a similar scenario within the past 2 weeks. I also had the diverter valve/turbo bypass valve go bad at nearly the same time due to it not holding a vacuum. Since it recirculates, the turbo boost leak test does not test the bypass valve function, it must be removed from the bottom of the engine.

Either way, both are now fixed on my car.

Doug

 

[midnightmekanik]

Just to understand the lockup problem a bit better, if this were the case, would it cause the gear to slip? And if so, wouldn't the RPMs surge since the car is accelerating -- that is, is a slip equivalent to being in neutral?

It wouldn't feel like a slip, it would feel more like bogging... Sort of like shifting into the next gear too early, then realizing it and shifting back to get rpms up. Similar feeling, but obviously not as drastic as it would be in a manual. When the TC goes into/out of lockup, it doesn't slip, even though it may sound and feel like it sometimes.

Have you tried keeping the trans selector in a lower gear? As in not putting it in drive? I don't have an auto vw, so I don't know if it would be 1-2 or S-L selections, but I think you get what I mean. I think tiptronic mode would even suffice to test the TC and if it's locking/unlocking.

 

[BusRider]

The "L" hose is indeed the source of my problem. Thank your for your insight!

My problem is back and I'm confident it is another boost leak. I've used a VCDS to log the requested and actual boost air pressure and the graph shows that I can't hold more than 5psi above the requested boost. At that point, the boost pressure drops coinciding with the loss of RPM and whooshing noise from the engine bay.

A second boost leak test found another damaged hose (a small elbow) behind the air filter box, part number 058 133 394 A (superseded by 058 133 394 F). It is attached to a check valve and a hard line that is ultimately attached to the turbo charger. After replacing the part, the boost leak test no longer produces any noticeable leaks, other than the expected air flow from the engine oil fill hole.

Unfortunately, I'm still losing boost pressure. My diverter valve holds vacuum, though I noticed that if the valve spring is not perfectly aligned when vacuum is applied, then it may not reseat itself properly and close completely. Perhaps this is the culprit, though I'll have to look for more damaged hoses attached to the valve, turbo, and intercooler too.

Will report back if I find something of interest!

 

[Tomvw]

Unfortunately, I'm still losing boost pressure. My diverter valve holds vacuum, though I noticed that if the valve spring is not perfectly aligned when vacuum is applied, then it may not reseat itself properly and close completely.

That would appear to be the problem.