Sluggish Beetle

I have a 2001 Beetle with ALH motor. It starts fine and runs fine at low RPMs. It is very sluggish at hogher RPMs and sometimes throws an error code. The error code is P1556 which indicates intermittent low boost pressure. I have done the following things:

1. New air filter
2. New fuel filter
3. Checked all vacuum lines for leaks
4. Verified vacuum at waste gate actuator
5. Replaced N75 valve
6. Looked for clogging problems in the intake near the EGR valve
7. Disconnected batter for 15 minutes to reset ECM

The problem persists. I am not sure where in VCDS to check the boost pressure but I believe it will be low due to the error code. I am out of ideas except that it needs a new turbo as it has about 270,000 miles on it. Any thoughts/suggestions would be greatly appreciated.

Limp mode. Unplug the MAF and test drive. If no change or runs better, new MAF.
See if the VNT actuator is able to move freely. If not, clean the vanes (a pain).
Also, check the snow screen for debris if you haven't done that in a while.

Yea, you can fix it.
Read here at the Ross Tech wiki
Internet diagnose;
2) Bad MAF or wires/connect
1) Stuck actuator or vanes.
Exercise the turbo actuator to see if it's stuck. Watch the thing when you start the car, it should move over (iirc it's like an inch or so, there are videos)
If you still have the factory vacuum tubes, I'd replace them all.

Thanks for your feedback! Actually I can feel a power fluctuation when it goes into limp mode. When I clear the codes and or reset the ECM takes it out of limp mode. If I pedal it carefully I can keep it from going into limp mode. But that is a terrible thing to do on the interstate. People get upset. I forgot to mention it in my original post but I did unplug the MAF sensor and it ran about the same. I check that the Waste gate actuator is not frozen up and it moves when vacuum applied. The turbo on the ALH does not have variable pitch vanes. It is controlled by the amount of exhaust sent to through the waste gate. It could be the MAF sensor as you suggest. Is there any way to test the sensor to verify that it is bad? I would rather not spend the money on a new one until I am sure that is the problem. I will also check the snow screen as suggested. (It is interesting that in all of the research I did that MAF sensor was not mentioned as a possible cause for a P1556 error.)

On highway, leave in gear, push the clutch in, turn off the car, turn on the car, let the clutch out, motor fires right up, very safe and easy. The ALH does have variable vanes, no wastegate, rather a VNT actuator. See that it does move when you start the car.
It's very possible all this stuff is working fine. If you can verify, you'll want to start examining wiring/connecters, a real pain.
There are loads of write-ups on MAF diagnosis, read carefully, many folks just replace when they see how easy it is. And you're right about the code not indicating MAF, but our little computer system is not that sophisticated, there are exceptions.
Todays thread from Drzaius for example.

dernster said:

Thanks for your feedback! Actually I can feel a power fluctuation when it goes into limp mode. When I clear the codes and or reset the ECM takes it out of limp mode. If I pedal it carefully I can keep it from going into limp mode. But that is a terrible thing to do on the interstate. People get upset. I forgot to mention it in my original post but I did unplug the MAF sensor and it ran about the same. I check that the Waste gate actuator is not frozen up and it moves when vacuum applied. The turbo on the ALH does not have variable pitch vanes. It is controlled by the amount of exhaust sent to through the waste gate. It could be the MAF sensor as you suggest. Is there any way to test the sensor to verify that it is bad? I would rather not spend the money on a new one until I am sure that is the problem. I will also check the snow screen as suggested. (It is interesting that in all of the research I did that MAF sensor was not mentioned as a possible cause for a P1556 error.)

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You are at 270,000 mi, so if you have never replaced the MAF it is probably due.
I question your statement that your turbo is due for replacement unless it leaks oil.

I know its on your list already but I would replace old vacuum hoses, go beyond checking them, clean vacuum fittings, double check the vacuum check valve, replace the vacuum hose going to the anti shudder valve. Watch for different diameter hoses.
I had a similar problem and it was cured by replacing the MAF with a new Bosch one but the vacuum system has the tendency to give you grief so leave no vacuum stone unturned. Good luck!!

Your actuator may move but I bet it's sticking causing your problems.
Get a mityvac and crawl under the car with a strong flashlight .
Connect the mityvac to the actuator and note when the lever starts to move.
Locate the stop and continue to apply vacuum till it hits the stop or stops moving, the actuator should start to move around 3-5 "of vac and be at the stop at 18".

It should also move smoothly, if it doesn't there lies your problem. You can excersise it with an open end wrench, I believe it's a 14mm or 9/16 . If it crunches it could be dirty vanes or a bad actuator, that can be replaced while turbo is on car and adjusted.

To see if it's the actuator or the vanes you can remove the circlip that holds the actuator arm to the lever and move the lever manually and the actuator with the mityvac.
The lever should flip flop back and forth with your finger and hit the stop, if not , again turbo needs cleaning .

The actuator should also move smoothly with vacuum applied, no ratcheting or jerking, if so need replacement. Just my thoughts.

I appreciate all of the input. I have ordered a new MAF sensor. It was a lot less expensive that I remember. If that does not resolve the problem I will do more extensive testing with the mityvac. I did test it with the mityvac earlier but only observed that it was not frozen and not what precise vacuum pressures when it started and stopped.

How much vacuum is your pump able to create? You need to be around the 24"Hg for proper turbo operation. I am willing to bet (if you have 270k miles on that car) that the nipple on your vacuum pump is loose and leaking and not able to maintain proper vacuum.

If you do take the actuator arm c-clip off use a piece of sewing thread tied to it when you re-install it.
I lost a couple in the body when they popped off as I was trying to insert them.
There's also a VW bulletin about the actuator rusting inside itself.
At this point its 2 easy nuts to take the actuator off.
Move the arm on the turbo to see if it sticks as it moves.
If so it needs cleaning inside, many posts how to do it.
I would replace the turbo only if you find something wrong s/a excessive shaft play (maybe a lot of oil in the intercooler) or the arm not moving freely after cleaning.

Check the hose that goes from the vacuum pump to the break check valve and brake booster.
I was getting occasional limp mode, that hose was cracking at the vacuum pump.
Cut the cracking part and adjusted the hose, haven't had much of an issue since, knock on wood.
Otherwise, what everyone else mentioned good to check.

I replaced the MAF sensor and the car runs the same. Still getting a p1556 error. I check the actuator. IT begins motion about 6 -7 Hg and stops about 13 - 14 Hg. It moves smoothly. Base on everyone's input I am going to:

1. Check vacuum at vacuum pump, brake check valve, and turbo actuator
2. Clean, lubricate, and exercise check valve and linkage.

I would rather not take anything apart if I don't have to. My big hands don't fit work well in tight areas. Everyone, thanks for the input. I am about ready to take it to my trusted mechanic but he is 3 hours away. I always do the DIY thing to its fullest extent before making the trip.

Try adjusting the actuator to open at about 4 (3.5 to 5.0 is spec), could make some difference.

You can't affect the vacuum required to start moving the actuator by changing the rod length, all it has to do is overcome the internal spring pressure in the actuator. The length mostly affects where the vanes end up in the no vacuum position. I think the spec to hit the stop is more in the 18in range though, which suggests you could lengthen the rod a bit. Also verify that the VNT lever is actually hitting the stop when you apply vacuum. It could be stopping short, and slow to open, due to carbon buildup in the internals.

If you have access to VCDS, or other logging tools, it is easy and worth it to check boost specified/requested, and the same for MAF. This can pinpoint when you are underboosting, whether it may be due to a boost leak, etc. Measuring Blocks -> Group 003 (MAF) and Group 011 (MAP)

I have verified that there is 20 Hg of vacuum at the actuator at idle. I am considering a new actuator. I did a lot of cleaning and lubricating of the linkage and performance is unchanged. I will definitely take a look with the VCDS to further pinpoint the problem. Rod adjustment seems like a good option as well.

dernster said:

I have verified that there is 20 Hg of vacuum at the actuator at idle. I am considering a new actuator. I did a lot of cleaning and lubricating of the linkage and performance is unchanged. I will definitely take a look with the VCDS to further pinpoint the problem. Rod adjustment seems like a good option as well.

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Lengthening the rod would help with over boost.
I had this if I was going up a long hill, I would easily get 20 lb boost.
I turned the adjusting nut over a turn the first time then a bit more at a time 2 or 3 times.
If you had the actuator off did you happen to shake it to check for loose rust inside?
VW bulletin on this.
Mine did not seem to have any but I replaced it to be sure.
I also sprayed a bit if penetrating oil in the N107 vacuum valve, shook it, then lightly blew it out.
The car seemed more responsive at low end and my boost went up again.
Seems good for the low end, bad for the upper end.
I have a new valve, just have to put it in.

I installed a new actuator and the performance seems slightly improved. I realized later that I had not adjusted the actuator rod length. When it arrived the lock nut was loose and when I installed it i had to turn the rod out several turns to get it to slide on. I neglected to go back and readjust it. I will be doing that when I get home tonight. Hopefully that will resolve the problem. Stay tuned..............

dernster said:

I installed a new actuator and the performance seems slightly improved. I realized later that I had not adjusted the actuator rod length. When it arrived the lock nut was loose and when I installed it i had to turn the rod out several turns to get it to slide on. I neglected to go back and readjust it. I will be doing that when I get home tonight. Hopefully that will resolve the problem. Stay tuned..............

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Did you measure the length between the 2 of them before you installed the new one?
My new actuator had paint on the threads indicating if it was messed with or not.
I still had to adjust it.
The vacuum pump setting is a good starting point.
The actuator should start moving at 3 inches vacuum, full at 18 inches (or so)

Sorry for the long delay in posting. A death in the family distracted me from this. The problem is solved. While installing the actuator I realized that the vanes in the turbo had a very small range in motion. I had the turbo replaced ( and injectors0 and is it running like a brand new car. Thanks to everyone that posted on this problem. I learned a ton and in a strange way had fun doing it.

That old turbo may be sailable. You can often free up the vanes and if the shaft is nice someone would buy it for a hundred or two.
If your replacement unit was brand new, they should not have needed the old one fore a core.