Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

Maf

the VAG COM scan got a reading of 120...I believe that is mg/h...what ever that is, at idle

transmission

I am still not sure if the transmission is ok....It still slips when I take off and jerks alittle at stops...but seems to shift ok at speed....The mecahnic I brought it to said he got no codes this time for the tranny,and that the shifting and jerking could be from a bad MAF.....I don't know

also I got a new code 1556 MAP sensor....I put Dielectric grease on the MAP when I put it the Intercooler back in..also on the MAF but Hva esince cleaned the MAF Plug and recheked it. Still no power.

rdkern said:

What's a throttle body?

What are the MAF readings? Sometimes the readings are different than expected, because the air flow is different than expected. How many miles on this puppy?

Also, it's a chore to read. Putting in line feeds at paragraphs and such makes for easier reading and understanding.

Click to expand...

Sorry....what ever you call the intake section where the CCV Hooks up

Vacuum hose

OK after the Mechanic reset the computer, he checked again and there was a low boost signal, and the MAP was reading 120 at idle.

the next day I tried driving it still low power and shifting issues, so UI tried disconnecting the Map and it was still the same...so while looking in there I noticed a vacuum hose that hooks up to around the intake or EGR was off.

I remember hooking it back up when I put it back together, but the clip I put it in made it tite so it must have came lose, or the Mech disconnected it trying to get me to leave it with him to fix the problem.

Anyway I hooked it up and the engine runs fine, it will rev to redline instantly in neutral, but I'm still having transmission problems.

The temp reaches over 200 ,is that normal, and it slips when I take off from a start and feels like a lose trailer when I come to a stop.

l_c said:

Bassewitz ... I'm no expert but it sounds to me like it could be some type of vacuum issue. Not sure whether that means, in the path to the turbo actuator. You may need to set something up that would allow you to monitor the MAP (actual) vs requested, right after initial start-up of the engine. The system goes into limp mode because something's not entirely right.
I don't know why, but my limp mode problem (on my 2002) had something to do with the EGR valve (replacing it fixed my problem). [ Replacing N75 didn't fix my issue. ]
I wouldn't assume that the door chime has anything to do with the limp mode. I guess it's possible, but I wouldn't assume that association because I know that those darned microswitches in the door lock modules are prone to not work (after a while). Larry C

Click to expand...

I have been gathering all my service records for the potential buyer and while scanning in some of the major ones I noticed that the vacuum hoses were replaced during the last major repair. I would post the entire report but at this point I am actually more interested if anyone thinks that this even qualifies as a limp mode or if this is something different.
Thank you everyone for your input.

Limp mode newbie

Well, with a 2002 Jetta it was bound to happen to me. I had the codes, experienced the symptoms, cleaned the MAF contacts, and decided I just didn't have the time to work up to the bad stuff. Besides, from all of the comments that I read, I was thinking turbo or turbo actuator. Brought it to a local shop with a good rep. He called back and said that it was, sadly, the turbo. The worst part is that VW has issued a TSB for that turbo and has come out with a newer part because of the problem that I am experiencing. That means pulling an old part isn't going to do it; it would have the same problem or worse. The damage $1,800 (a coolant sensor needed replacing; I knew about that). With 70,000 miles on it and a new timing belt, I just couldn't walk away from it. So I'm going to try to get 3 more years out of it. But as God is my witness, no more turbos in Minnesota, no more German cars, no more VWs in my lifetime. There are only two positives that I can say about the car: 1)I only grow concerned if the MIL light is off, 2)and this forum, which has come to my aid many times.

Has anyone else heard of a TSB on the turbo of the ALH's? Perhaps I just don't read enough, but this is a surprise to me. I'm not confident in the diagnosis.

Thanks!

Thanks for the great info Can Grizzly! I worked through most of the stuff and found several things to check/replace/repair. Changed vacuum hoses, found stuck VNT actuator, found badly plugged EGR, found clogged up intake, etc. Lots of good projects! Really getting to know my TDI!
Have a great Easter,
Nick

Welcome Nick! I just compile the great information from this site. Let us know if you need more assistance.

My vacuum actuator does not hold vacuum. Purchased a new garrett actuator and proceded to remove the old one. After spraying the bolts with fluid the first one twisted of no problem. The other one rounded off easly with a box wrench. Attempts to loosen nut have failed. Does anyone have advice? This is a 99.5 tdi jetta with just shy of 200k miles. This nut is rusted pretty well.

Follow up on turbo

I picked up my 2002 jetta from Phoenix Auto in St. Louis Park Minn. Their estimate was exactly what they told me (~$1800, new turbo and a unrelated sensor change). When I asked them more about it, the guy said, "Want to see it?" Definitely a bad actuator. Mechanic Mike stopped by and said if they could have replaced just the actuator, they would have, but VW has changed the part and does not sell the actuator alone anymore. If one had time, one could locate and pull it off a junked Jetta, but then you might run into the same problem. I forgot to ask about the TSB. Sorry.
I liked these guys, and they knew VWs. Mike referred to another customer who had a 2002 whose timing belt went after a dealer install. I would try them again (and no doubt will have the opportunity to do so; I still have the glowplug harness to deal with, but that can wait until fall). The joke in my family is that between my wife's Prius and my Jetta we have, on average, a car that accelerates normally. After reading in the paper about a guy who just spent $1200 on his car's front end from hitting some of Minneapolis' finest potholes, I'm feeling slightly better about this expense. But not much.

Sorry bruemmer but you got taken by the dealer... I specifically mention in the original post hat you can purchase the actuator separately and dealers will try to sell you a new turbo to fix the problem. If you have the moxie you could show them all the vendors that would sell it and the fact is you may have replaced a perfectly good turbo.
www.tdiparts.com
www.boraparts.com
www.worldimpex.com
Are a few trusted vendors in the US.

I had Langen VW in Meriden,CT replace my vaccum actuator today. I could not get the old one off.They showed me the old actuator that was full of loose rust and made noise like a childs rattle. No wonder why it didn't work. The new one was installed and now it runs great. Hats off to the repair people in Langen VW...I am happy the limp mode finally is gone. Runs like new.

99.5 Jetta TDI 5 speed
192000 miles

I'm experiencing limp mode every week or so during my 100mi daily commute. Will update this thread when I get it fixed, not sure which of the several elements is causing it.

bassewitz said:

I have been gathering all my service records for the potential buyer and while scanning in some of the major ones I noticed that the vacuum hoses were replaced during the last major repair. I would post the entire report but at this point I am actually more interested if anyone thinks that this even qualifies as a limp mode or if this is something different.
Thank you everyone for your input.

Click to expand...

I just heard back from the buyer of my car. He owns a shop that fixes fuel injection pumps and turbos.
The final result was not any vacuum leaks or electrical shorts. Here is what he told me:
"The injection pump and injectors were removed and tested: the pump fuel output was approx 5% low, and the injector opening pressure was low, with one injector having a partially blocked spray hole. We re-calibrated the injection pump to the top of spec, and installed new nozzle tips in the injectors."
Yes, the dealership had tried that something similar.
"[...]ran vehicle with separate fuel supply connected directly to injection pump, bypassing vehicle fuel supply system, [...] swapped good injector from a donor vehicle [...]"
Not sure why it worked now. My loss, his gain.

I am getting a buzzing/humming noise from my N75 valve that is somwhere between a bumble bee and a humming bird sound. Replace it? To be more specific I get the noise directly after turning the car off.

Make this thread a STICKIE!!!

This thread should be STICKIE....maybe I'll start a poll!!

My limp mode issue evolved into a more serious problem with the check engine light coming on, and isn't fixed for more than a few minutes by cycling the ignition.

Guess it is the MAF or possibly the N75, and will take it into Tomas Sport Tuning late this afternoon for work tomorrow. Will update thread when I get it fixed...

Per Tomas Sport Tuning it was the N75. If that turns out to not be the fix, I'll update this forum.

unexpected limp mode cause...

I just wanted to chime in after I found the cause of my overboost situation. I was getting limp modes every time I would accelerate past 2500 rpm in 3rd, 4th and 5th gears. Virtually no turbo presence to mention of at all times. I got started with diagnostics with this thread (thanks CDN Griz!) I have a 2002 Jetta 225k miles with rocketchip stage 1, stock turbo. With the miles on the car, I opted to change all the vacuum lines. No effect. Test the N75 with Vag Com. It's dead. Swap it for the N18. Dead too. I changed the N75 (EGR is deleted so I didn't bother with the N18). No effect. Hmmm . Hook up a vacuum pump to the VNT actuator. Can't pull a vacuum, IE the rod doesn't move at all. Bad actuator or stuck turbo vanes? I take a chance with the actuator and order one. Bingo! The old actuator was stuck.. the rod came loose from hitting it on the ground with a big puff of rusty smoke. I move the rod on the turbo for the vanes and it's moving freely whew! I install the new actuator. No effect.

I am now at wits end. I omitted the vacuum test on the lines Grizzly mentions at the beginning of the diagnostic procedure. So I start checking for vacuum leaks. I found the brake booster line to have cracks in it at both ends. I replaced the plastic line with air compressor line I had laying around. No effect. Then the only source of the problem and the one that cause all the other failures... the boost valve ( http://boostvalve.com ) I installed after the Rocketchip. I unplug it and bang! Turbo is back.

I emptied the intercooler of oil 2 weeks ago, poured almost 2 cups out of it. This oil made it's way into the line leading to the boost valve. I took the valve apart to clean it and black particles of dried oil came out. I did the same with the line... even worse. I hope this experience can help others...

I'm done with trying to fix this limp mode issue..Picking up new 2010 Jetta TDI sport wagon DSG Trans..I hope it will be some time before I have any issues...
99.5 was getting bad.

Related question on this: is just cycling the ignition switch while driving otherwise bad for the engine? My owner's manual ('03 ALH) makes a big point of not bump-starting the car, but warmed up and turning at 2k rpm might be a different story. Any opinions?

The one time I've needed this, I idled it, shut it down, then used the starter to bring it back and let it stabilize at idle before picking up the load again. More than happy to hear I'm being paranoid here!

werdna said:

Related question on this: is just cycling the ignition switch while driving otherwise bad for the engine? My owner's manual ('03 ALH) makes a big point of not bump-starting the car, but warmed up and turning at 2k rpm might be a different story. Any opinions?

The one time I've needed this, I idled it, shut it down, then used the starter to bring it back and let it stabilize at idle before picking up the load again. More than happy to hear I'm being paranoid here!

Click to expand...

Not hard on it at all... drive more, worry less!

Mine was REALLY simple but caused ALOT of delays and heartache coz I didnt have a diagnostic unit! All it was, was a faulty connection to the injector sensor - when I finally found a place that could read the trouble codes (Zimbabwe is tough!) they repaired the connection and cleared the trouble code. All back to normal

I have a very situational limp mode isue (po234): It happens on 2 occasions almost the exact same place.
1. Hill climbing at high altitude (about 8,000ft); about 60-70% throttle, 15psi of boost.

2. After engine breaking (coasting down hill in gear)

I believe my tune is good for 18psi. My boost valve stops a spike at 21 and regulates sustained boost at 19psi. I cant get it to hit limp mode at full throttle.

Last summer I replaced all vaccume line and n75 valve and replaced the MAF. My acutator will blead 1" vaccume over 5 or 10minutes.

Any ideas?

So I threw a p0234 code again today. This time I pulled a log in vag com before clearing it.
Here it is:
Tuesday,09,March,2010,17:30:45:51785
VCDS Version: Release 908.1
Data version: 20091018
--------------------------------------------------------------------------------
Readiness Status: 00000000 00000111 10000000 00000000
MIL Status: MIL OFF
Comprehensive Components: Passed
Fuel System: Passed
Exhaust Gas Recirculation: Passed
Number of EOBD-related DTC(s): 0
Tuesday,09,March,2010,18:29:16:51785
VCDS Version: Release 908.1
Data version: 20091018
--------------------------------------------------------------------------------
Address 01: Engine (038 906 012 CP)
18:29:10 Group 003: EGR
903 /min Engine speed 870-950 rpm
500.0 mg/str MAF (specified) 230-370 mg/H
425.0 mg/str MAF (actual) 230-370 mg/H
4.8 % EGR duty cycle 40-75%
18:29:10 Group 011: Charge Pressure Control **Done at WOT**(See label file)
903 /min Engine speed rpm
999.6 mbar Specified MAP 1850-1950 mbar
867.0 mbar Actual MAP 1700-2080 mbar
19.9 % D.cycle MAP v. 45-95%
Thursday,27,May,2010,17:05:45:51785
VCDS Version: Release 908.1
Data version: 20091018
--------------------------------------------------------------------------------
Freeze Frame Data for address 10
PID02 DTC that caused freeze frame data storage: P0234
PID04 Calculated load value: 49.0 %
PID05 Engine coolant temperature: 86 ∞C
PID11 Intake Manifold Absolute Pressure: 154 kPa abs
PID12 Engine RPM: 2094 /min
PID13 Vehicle speed: 91 km/h
PID14 Ignition timing advance for cyl #1: 10.0 Degrees
PID15 Intake air temperature: 34 ∞C
PID16 Mass Air Flow: 51.20 g/s
PID17 Throttle position sensor: 47.8 %

Yes that's 22 psi of boost *** BUT *** The mc nally boost gauge only recorded a spike of 13 psi.
The group 11 Actual Map mbar of 867 is appropiate for my altitude. (the sensor is working. I think)
So which gauge is right? stock map or Mc Nally??? The mc nally gauge is less than 1 year old and shows appropriate values at full throttle.
I wish I could see what N75 cycles were leading up to the event.
...Buler?

Thorne said:

Per Tomas Sport Tuning it was the N75. If that turns out to not be the fix, I'll update this forum.

Click to expand...

Hopefully got a final fix on my mysterious overboost / limp mode problem -- Tomas cleaned out quite a bit of caked sulphur from the intake area. After a little testing I'm unable to get it to fail once warmed up at high RPM's, where before I could get it to replicate pretty well on my 100 mile commute when punching it hard above 70mph. It also would fail when towing up steep grades with heavy acceleration.

So, after replacing the MAF (just on spec = my idea), N75, and testing all the vacuum lines, it looks like gunk buildup on the intake side was to blame.

As before I'll update this Forum if it turns out to be anything different.

Well, I will relate my experience and see if anyone can help. I may help someone else in the process. BTW, thanks for all the extremely valuable input. This site has saved me thousands.

I read this thread several times. Was having limp mode, mostly without throwing a code, on long hill climbs. I have several on my 100 mi. RT commute. Occaisionally got 1556.

2002 Jetta, 237K miles. Snow screen removed.

I started going through the procedure.

Checked MAF with Vag-Com and replaced MAF. Slight improvement in power, still have limp.

Check vacuum with Mityvac at N75. About 24" Hg.

Test N75 with Vag-Com. OK

Test Actuator with Mityvac. OK, holds vacuum. Adjustment appears to be in spec. Turbo moves relatively freely with no real bind through entire range of motion. I have had the turbo off several times (every 6 mos., but not since 1/2008) for carbon buildup cleaning after running B100. Now run about B20-B40. That failure was different and I got where I could feel it coming on. It would throw a CEL consistantly. Switch to petro 100 for a month or two cleans it out.

Run LM Diesel Purge. Replace air filter (had K&N since about 88K mi.) Glow plug harness (was getting consistant codes), fuel return lines, vacuum lines with McMaster silicone (except for rubber line to turbo (ran out of line). Slight improvement in power, still have limp.

Replace main vacuum hose to brake booster after finding a split in the hard plastic line at the check valve. Virtually no change.

Clean intake and intercooler. Heavy carbon buildup in EGR and intake manifold. Very small amount of oil in intercooler (EGR cycle recal at 119K mi.) Found 66% missing gasket on driver's side of exhaust cooler. This was causing a whoosing sound on accel. Replaced. Whoosh sound fixed, signficant improvement in low-end acceleration. Turbo whistle is good. Boost guage shows up to 16 psi. So far, no more limp mode.

Now, the reason for my post. While the car has significant improvement in low-end accel., it still feels sluggish on the long hard hill climbs. It will do 75mph, but cannot accelerate up the hill, even at WOT, like it used to. I have verified all is well on the intake side. My next thought is some sort of restriction in the exhaust. Thoughts?

Thanks for all your help.

Clarification:

taugust said:

. It will do 75mph, but cannot accelerate up the hill, even at WOT, like it used to. I have verified all is well on the intake side. My next thought is some sort of restriction in the exhaust. Thoughts?

Click to expand...

So, you are boosting 16PSI while going up that hill, WOT, and can't accelerate? ?
Please clarify...........