Poor power after limp mode fix kit and EGR delete

Hi All -

New to me 2003 ALH Jetta 5spd, currently 427,000 Km on the ODO.
It ran ok after acquiring it, a little smokey on startup, and consistently went into limp mode once the engine was warmed, more so on a hot day. When not in limp mode - power was as expected, just enough to make it peppy around town and give me confidence for highway passing power. If I ran the heater on high, fan on high to shed engine heat, then limp mode was usually avoidable. Drove it like this for a couple months this summer until I had time to get the car in my garage and do a bunch of work/PM.

Fast forward to this last week, I was finally able to find time to get the car into my garage and leave it on stands for a few days while I did the following work:

- Oil/filter change
- Transmission fluid change
- Fuel filter change
- Air filter change (and snow screen cleaning, it was TERRIBLE!)
- Diesel purge procedure/treatment
- EGR cooler delete (no physical race pipe)
- MAF replacement
- N75 replacement
- One way check valve replacement
- Vacuum line replacement/reroute (as if running a race pipe)

Now, after all this the car definitely runs better at low power level demands, but seems to be lacking full boost when called for. I'd say it's half way between limp mode and normal stock power. Passing power on the highway is really lacking now. I have no engine light on the dash, but I will check for any lingering codes soon. It feels as though the fuelling is fine, but the boost isn't kicking in.

I do not have VCDS for this car (yet).

I have a new turbo actuator sitting in the garage but haven't replaced it yet. The actuator on the car seems to move the same as the new one in the box, judging by 'finger force' required to move each! I hesitate to think its the actuator, only because boost levels seemed fine prior to this work I did (except when in limp mode).

I plan to borrow or purchase a vacuum hand pump to check for vacuum leaks on all the vacuum line replacements I just did. I also plan to build a little boost tester device out of some plumbing supplies.

In the meantime, can anyone point me in the right direction to get this sorted before I can get my hands on VCDS? Does the fact that high heat levels induced limp mode mean anything to anyone??

Thanks in advance!
-Jason

It seems like your doing a lot of tossing parts on it without correctly diagnosing. Since the MAF, N75 and check valve don’t go bad all that often and are easy to rule out.

With VCDS you can actually graph your boost to see what really happening, which makes a huge difference. As for diagnosing right now, start the car and remove the vac hose from the n75 going to the actuator. Reach down and put your hand on the arm, with your other hand, put the vac line on and off the n75, this will move the actuator and you can feel how smooth it is. Making sure it’s not sticking and has full swing.

I’m suspecting, when things are hot, the metal expands in the turbo and caused sticking vanes. Which is the most common issue.

Personally, I would stop just adding parts, and start actually diagnosing. It will save you time and money on repairs in the long run.

An excellent step-by-step low power/limp mode troubleshooting guide:

http://forums.tdiclub.com/showthread.php?t=179589

keaton85 said:

It seems like your doing a lot of tossing parts on it without correctly diagnosing. Since the MAF, N75 and check valve don’t go bad all that often and are easy to rule out.
With VCDS you can actually graph your boost to see what really happening, which makes a huge difference. As for diagnosing right now, start the car and remove the vac hose from the n75 going to the actuator. Reach down and put your hand on the arm, with your other hand, put the vac line on and off the n75, this will move the actuator and you can feel how smooth it is. Making sure it’s not sticking and has full swing.
I’m suspecting, when things are hot, the metal expands in the turbo and caused sticking vanes. Which is the most common issue.
Personally, I would stop just adding parts, and start actually diagnosing. It will save you time and money on repairs in the long run.

Click to expand...

I'm not a fan of tossing parts on all at once, but I am bound by time availability lately. I had no choice but to get as much work done all at once simply for time efficiency. I knew though, that it may make diagnosing a little more tricky down the road . . . and here I am now!

Thank you for the advice on monitoring the actuator while I remove and replace the line to the N75, I will try this soon and report back. You suggest watching/feeling the arm for smoothness and travel . . . will I get full travel at idle with no load?

I don't plan to add any more parts without further diagnosing. Hence, here I am asking for advice. I appreciate anything and everything folks have to offer without the assistance of VCDS right now!

To clarify my comment about the heat-induced limp mode . . . that is no longer happening. The heat-induced limp mode hasn't happened since all of the above work was performed. To clarify further, I don't think I have limp mode happening right now. It is just full-time reduced power (suspected boost). Fuelling seems to be fine, as I can flare the RPM's and reach higher top speeds than limp mode would allow me too (but, it is now very sluggish on the top-end).

Vince Waldon said:

An excellent step-by-step low power/limp mode troubleshooting guide:
http://forums.tdiclub.com/showthread.php?t=179589

Click to expand...

Thank you Vince.
I will peruse and do what I can with what I have available in mine and neighbours garages!

To start, as per advice in that post I will unplug the MAF sensor before my drive home tonight, and see what kind of results I get.
(I suppose it's possible the new Bosch MAF I replaced is bad out of the box . . .)

Anti shudder valve maybe?

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WildChild80 said:

Anti shudder valve maybe?

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Click to expand...

You mean it might be stuck in the closed position? I thought about that too.
The ASV is the round flap/plate visible from passenger fender when the 90 degree intake elbow is removed, correct? Controlled by the top side 'silver vacuum puck'??

If so, then i'm sure it is open. I recall seeing it in the open position when replacing that short 90 degree intake hose . . . but these last days have been a whirlwind for me so I will double check and confirm tonight.

Without vcds it's a little harder to diagnose without known good parts, you haven't mentioned your map sensor, I realize they also rarely go bad but short of a somehow stopped up intercooler or asv that partially closes under requested power(yes totally unlikely/nearly impossible) I am at a loss. Have you taken a good hard look at the rest of the boost pipes?

Might be sticky vanes too...you need to get a list of proven good things and start a list of not proven good points and start looking at what indications you would get from a failure of each. It's not improbable that you don't have 2 small issues causing a weird situation like a map sensor not reading accurately and a boost leak that the map sensor doesn't know about because it's reading more boost than it's actually making.

Have you cleaned your intake?



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WildChild80 said:

Without vcds it's a little harder to diagnose without known good parts, you haven't mentioned your map sensor, I realize they also rarely go bad but short of a somehow stopped up intercooler or asv that partially closes under requested power(yes totally unlikely/nearly impossible) I am at a loss. Have you taken a good hard look at the rest of the boost pipes?

Might be sticky vanes too...you need to get a list of proven good things and start a list of not proven good points and start looking at what indications you would get from a failure of each. It's not improbable that you don't have 2 small issues causing a weird situation like a map sensor not reading accurately and a boost leak that the map sensor doesn't know about because it's reading more boost than it's actually making.

Have you cleaned your intake?



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Click to expand...

I have looked at all the boost pipes I can see, and tugged on any I can reach to check for clamping power. All seems well, but I plan to make a little boost test device I can hook up to my air compressor . . . a project for another day.

Intake has not been cleaned . . . and I probably won't clean it . . . I might just replace it with a readily available PD150 or similar intake. (extra cost yes, but downtime reduced; possible benefit of airflow for future mild/moderate performance upgrades once all PM is squared away).

Again, I seemed to have full power BEFORE swapping parts for limp mode . . . so if it is the intake or MAP then it might just be coincidental timing.

I don't usually believe in coincidence but these cars sometimes have very convenient timing

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the most common issue of all is sticking vanes, then vac lines (including brake booster hose) then the actuator. So before doing anything, checking the movement of the actuator is a 5min job and will determine a lot.

Intake cleaning is a very easy job and shouldn't take more than an afternoon, but once more important in my opinion is cleaning the intake ports on the head!

Put the old MAF back in and see if your power is restored.

I checked codes with a QPro, and came up with:

17964/P1556 - Charge Pressure Control: Negative Deviation

19560/P3104/012548 - Valve for Intake Manifold Flap (N239): Short to Plus

16486/P0102/000258 - Mass Air Flow Sensor (MAF/G70): Signal too Low

I'm not sure if these codes were from before or after my parts swaps. As such, I have swapped back to the N75 and MAF that came on the car. I'm going to start from scratch, (kind of), and refer to the previously linked post about diagnosing low power/limp mode if it returns.

I've only driven the car less than 100km since clearing codes and swapping back to the old parts. Drivability seems improved, and turbo seems to boost (maybe marginally) better. No CEL has returned, yet. EGR cooler will remained removed, with the vacuum rerouted accordingly, eliminating the N239 and N18 entirely.

If anyone has further helpful advice at this point, I'll take it! Otherwise I'll report back as things change. I'm also planning on acquiring VCDS for the MK4, as well as a vacuum gauge/hand pump to check for leaks/test pressures etc.

It's been a couple days worth of commuting, no return of limp mode or engine codes...yet.

Seemingly, all is well.

The N75 and the MAF..... is it possible for these to slooowwly go bad? Or, do they just work properly for their lifespan, then stop working suddenly?
(ie. Are they like an on/off either they are working or they aren't, or rather can they still be working...but poorly?)
Can they be bench tested in any way in the home DIY garage?

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From my experience, they slowly go bad most of the time. The maf will slowly start to read less and less on the high end. Best way to test it is to do a hard pull in 3rd and watch your maf actual. Should exceed 800 easily.
As for the n75, typically it'll leak vacuum is all. It's cheap enough to just replace if you think it's going out.