intermittent fluctuating idle - mostly when cold hard to diagnose

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
Hi guys - need a little help here. I've searched everywhere and found some leads but all dead ends. Here is the situation:

2004 BEW Jetta Wagon. 274,000 miles - all original engine components. Meticulously maintained by the book. Mobile 1 TDT since 80K Miles. All 505.01 before then. Changed every 10K miles.

About 3 months ago I got a MAF code - implausible signal P0101. Replaced MAF - this is my third and know they do go bad - had this one in the car of about 10 years. Error comes back with new MAF. intermittent error code. comes and goes. engine runs fine. fuel consumption is fine. I disassemble and clean EGR - it was gunked up but not that bad. MAF error light is now off - may come back.

At about the same time my engine started to have an inconsistent idle which MOSTLY occurs when the engine is dead cold. Runs fine otherwise and rarely occurs when warm. Engine will decrease idle by a bit and then blip over 900rpm and settle back down. Does this cyclically/irregular about once per second. It is very noticeable. Does it most of the time when cold. It has done it a bit when warm though much less likely.

There was no change/maintenance the coincides with this behavior. Just started one day. This behavior didn't grow into this problem. One day it just started.

Here is what I did - Checked Rosstech VagCom - did notice idle adaptation was significantly off (Per other threads I read) when this was occurring for cylinder 1 and 3. When the engine was idling smooth, there was still a bit of adaptation on 1&3 but it was what I would consider normal for an engine of this vintage. don't remember the exact values but they more closely matched across all four cylinders.

Checked the full intake for any air leaks/faulty connections - didn't find any. Engine air filter is newer (3000 miles on it) but I do see some oil weeping around the connections leading to the intercooler and to the turbo. This is the original turbo.

Checked for any vacuum line leaks - no sign of any.

Checked coolant temps with VagCom - all were in spec and reading correctly.

No engine ticking/knocking but still have to remove the valve cover to check cam lobes - still original cam and injectors.

Theories: Considering this mostly happens when cold could this be:
1. turbo failure - oil leaking around bearings into intake - only takes a few drops here and there to get consumed by engine. at higher RPMS the turbo seals up under load and as it warms up tolerances close off the leak?
2. Vacuum leak due to a connection that gets tighter when warm? Could this be intake plumbing issue as there is a coinciding MAF error code that intermittently pops up.
3. Cam is failing and may need to be replaced? But if this is the case what would things change with engine temp and wouldn't this grow over time instead of all at once?

I love this little car - she's been good to me and owes me nothing but I need her to last me one more year and I'd love to join the 300K mile club. Any insights and guidance you guys can provide will help. I'll post pics of the cam and VAGCom readings tomorrow. I hate these intermittent issues!
 
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DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
I was wondering if it's possible I'm getting air into the fuel system somewhere? No fuel leaks I can see and seems unlikely given it's a pressurized system. However when I recently did a LiquiMoly diesle purge injector clean I did see a lot of air bubbles on the return line but more than likely from connections loose on the intake. I did the Diesel purge as a means to try and fix this issue.
 

1975 Kombi

Veteran Member
Joined
Jun 3, 2014
Location
Acton, Ontario, Canada
TDI
2003 TDI Jetta, 2011 Touareg TDI, 1992 D Jetta, 1992 TD Jetta, 2001 NB TDI, 1992 Golf coupe D
If you unplug the MAF does the idle level out? I believe the MAF also controls the EGR function.
 

Tdijarhead

Top Post Dawg
Joined
Nov 10, 2013
Location
Lawrenceville PA
TDI
2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Wife’s car, 2005 Golf TDI Mine, all 5 spds
Disconnect the upper hose leading from the egr to the intercooler. Just disconnect it where it goes into the egr. Do you hear a bup bup bup sound with the car running? That is usually a bad cam. Next remove the valve cover to actually verify a bad cam. If you’ve never had a valve cover on a PD off the cover is fairly easy to remove but because of the way the cam is set up as compared to an alh the internals under the cover look intimidating.

I’ve used pentosion 5-40 since I got my 05 at about 142k miles. I have replaced the cam twice and I’m at 455k now. When you sort out which are the cam lobes look closely and run you finger over them. Each lobe should be chamfered along each side, cam wear removes that chamfer and makes the edges sharp which you can feel with your finger.

I noticed no difference with engine temps and I have an ultra gauge that I’ve used for several years.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
If you unplug the MAF does the idle level out? I believe the MAF also controls the EGR function.
I'll try that the next time it happens. Hasn't for the last 3 days...very infuriating. Engine has been very smooth all weekend.
Disconnect the upper hose leading from the egr to the intercooler. Just disconnect it where it goes into the egr. Do you hear a bup bup bup sound with the car running? That is usually a bad cam. Next remove the valve cover to actually verify a bad cam. If you’ve never had a valve cover on a PD off the cover is fairly easy to remove but because of the way the cam is set up as compared to an alh the internals under the cover look intimidating.

I’ve used pentosion 5-40 since I got my 05 at about 142k miles. I have replaced the cam twice and I’m at 455k now. When you sort out which are the cam lobes look closely and run you finger over them. Each lobe should be chamfered along each side, cam wear removes that chamfer and makes the edges sharp which you can feel with your finger.

I noticed no difference with engine temps and I have an ultra gauge that I’ve used for several years.
I'll do that tonight...didn't have time this weekend to do it. I've taken the valve cover off before to inspect cam - so familiar with the activity. Hopefully it's not a bad cam but I just hit 275,000 miles so I'm probably due on this factory original cam
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Tiny charge air leaks start with MAF DTCs before a low boost DTC. And they are worse when cold. Smoke machine works great to track them down. Often it is the charge air hose fittings or the intercooler itself, where the duct rubs a hole through the core.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
Tiny charge air leaks start with MAF DTCs before a low boost DTC. And they are worse when cold. Smoke machine works great to track them down. Often it is the charge air hose fittings or the intercooler itself, where the duct rubs a hole through the core.
Thanks - I was going to use a smoke pencil to see if I can track down any vacuum leaks which is pretty straight forward.....open to suggestions on how to smoke test the intake as I guess I need to pressurize the air/smoke into the system looking got leaks. Any suggestions for best device to use would be appreciated. I'll be going over it carefully this week after I get it on the lift.. Just put new struts on the front. Car runs great otherwise. Just want to eliminate this issue and keep driving. Hit 275,000 miles on the morning commute. 19 years old.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
UPDATE - SO I am still experiencing this issue with no real solution in sight. A few more observations. AS stated the issue is intermittent - happens MOSTLY when cold. when occurring - If I blip the throttle it goes away for 3-5 seconds and then starts back up. Sometimes it goes away entirely.
I cleaned the EGR - it was dirty but not terrible. Wonder if maybe it's getting stuck open a bit at idle at times causing this. Blipping the throttle causes it to reseat and close? No leaks on the intake or vacuum lines to report.

Also - reading osme other posts here are some additional details about the car:

When I did my Diesel purge I did notice air bubbles in the return but not certain if that was dur to poor suction line connection
The in tank fuel pump is easily 15 years old and has 240K miles on it. Could it be starting to get weak and fail - poor fuel delivery could cause this me thinks.
The engine fuel pump is original and now has 20 years and 278K miles on it.
I replace the fuel filter by the book - every 20K miles with Mann.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
Air intake filter/box is clean.
New MAF - replaced assuming it had failed.
Wiring and connectors all look good.
I can hear the in tank fuel filter before startup when key ios turned to ON. replaced it at ~40K when it was making odd noises as preventative measure.
I'm due soon for a new fuel filter - so I'll replace that - maybe there is a restriction there? But why only at idle. above idle the car runs perfect.
 

zslnk

Veteran Member
Joined
Sep 4, 2006
Location
ON, CANADA
TDI
E320 CDI, 3rd gen Cummins 2500, ALH Sedan
Is your throttle flap sticky? The grease inside mine turned hard. The throttle flap is used to make a restriction to draw EGR flow in and during shutdown. I pried the back off the case, cleaned it and put it back together. Mine would cause idle dips and sometimes a low speed, off idle, driving issue when cold.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
Update:

Issue still exists and is now repeatable 80% of the time. Here is what I've done but the issues is still there and I am at a loss for the reason.
1. Replaced 18 Year old in tank lift pump - no change
2. Smoke tested the entire intake system at multiple points and all accessible vacuum lines. No indication of any loose connections or leaks in any tubing.
3. Cleaned EGR valve.
4. Took off and tested the intake flap/throttle body - operating normally - easy to move.
5. Completed 280,000 mile service - new engine air filter, fuel filter, oil change.
6. Completed 2 Liquimoly injector cleanings - pure liqimoly for 20 min each session
7. Ran engine off fuel in glass container to check for air bubbles in fuel - no air getting in the fuel system on the return line.
8. Replace fuel temp sensor about a year ago trying to get rid of hard warm start issue.
9. Drove the car with VagCom - logging Turbo requested and output - turbo producing boost and output tracking at or close to requested.

I still have hard to start when engine is warm - requires 2+ seconds to start.
And the idle fluctuation is still there. Slightly noticeable without AC and VERY noticeable with AC on. Load on idling engine causes this and it will fluctuate +/- 200 RPMs. It is there 90% of the time. Yesterday there was a while where it simply wasn't happening. Idle was smooth as silk. Other than this the car drives and runs fine. No issues at above idle. MAF light does come on periodically then goes away after about a dozen starts. Typically will come back on when the idle fluctuation is really bad. I think MAF is a false indicator and indicated the erratic nature of the intake air charge when this is happening.

I have noticed exhaust smell/fumes from under the passenger section of the car - like there is an exhaust leak - put it on the rack last night - no noticeable holes/breaks in the exhaust plumbing from the flex portion back to the muffler. Perhaps I have a broken EGR/Pipe/Connection? Would that cause this?

I'm at my wits end here and ready to take it to a local shop/expert. I need this car to last me at least one more year. Any and all assistance advice is appreciated.
 

mittzlepick

Veteran Member
Joined
Mar 18, 2001
Location
union maine
TDI
2004 jetta wagon (365k)2001 wagon tire burner 6spd 2003 wagon(417k)
Cam sensor? Mine gave hards starts for a month before giving that code
 

zslnk

Veteran Member
Joined
Sep 4, 2006
Location
ON, CANADA
TDI
E320 CDI, 3rd gen Cummins 2500, ALH Sedan
You can unplug the EGR electrical connection and see if the idle dipping is related to EGR cycle. You'll get a MIL but this is OK. Drive the car for a bit and see what it does with the EGR disconnected.

With my BEW, since new, I could sense when EGR was active. As the car aged I ran into the throttle flap issue and EGR getting sticky which made this more noticeable. A BEW with a tune that omits the EGR will run very steady.
 
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DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
zslnk - I'll try that this evening on my commute home. I might have tried that a couple of months back but I think that was with combination MAF and EGR....I'll unplug the EGR tonight and drive it to report back.
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
Zslnk - you win! I unplugged the EGR before my commute home. Car ran smoother than it has in a long long time. Idle is locked in at 903rpm. Smooth. Absolutely no fluctuations after 40 miles of mixed highway/local street driving. AC on or off. Low RPM driving is smoother than before with no more odd vibrations. So pleasant to drive now!

Also my warm start issue seems to be gone as well as the heavy exhaust smell from the back of the engine/under the car seems to be gone as well.

Now the question is what is broken/clogged/at issue that needs to be fixed. I'm guessing something in the EGR system is fouled up/broken/not working correctly. The EGR parts aren't cheap to get and replace... so I'll accept whatever advice anyone has. I'd like to keep the stock config and programming. Car has 280K miles and still running so I'd like to keep it that way
 

burpod

teh stallionz!!1
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Nov 27, 2004
Location
cape cod, ma
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82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
just delete the egr/maf. madness. get rid of the total POS bew intake mainfold and asv and just get a pd150 and delete ASV/EGR. better yet do that and delete MAF at the same time and get a real tune

the intake flaps and all that BS is just a headache. seen it too many times. you can pay big $$ and replace it as is, or gut it, and live life better.. your choice
 

DrewJetta

Member
Joined
Jan 24, 2023
Location
Cheshire, CT
TDI
04 Jetta Wagon
just delete the egr/maf. madness. get rid of the total POS bew intake mainfold and asv and just get a pd150 and delete ASV/EGR. better yet do that and delete MAF at the same time and get a real tune

the intake flaps and all that BS is just a headache. seen it too many times. you can pay big $$ and replace it as is, or gut it, and live life better.. your choice
Hmmm after doing a little online shopping around - I am more inclined to do this. especially after running the car for over a week now with the EGR disabled. I'd be interested in recommendations for a kit and tune...
 

CharlieTDI

Member
Joined
Jan 25, 2004
Location
UK
TDI
Golf 2002
For the fluctuating idle, have you checked the Coolant Temperature Sensor (CTS) ?

I had a similar problem with fluctuating idle when cold. The car also revved to ~2-3k RPM when starting, but generally only when cold, and not all the time.

Replacing the CTS fixed both the high rev starts and fluctuating idle.
 

J_dude

Veteran Member
Joined
Jan 9, 2020
Location
SK Canada
TDI
2003 1.9l “Jedi”
just delete the egr/maf. madness. get rid of the total POS bew intake mainfold and asv and just get a pd150 and delete ASV/EGR. better yet do that and delete MAF at the same time and get a real tune

the intake flaps and all that BS is just a headache. seen it too many times. you can pay big $$ and replace it as is, or gut it, and live life better.. your choice
Does the BRM intake manifold fit the BEW? Those are easier to find than PD150
 
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