2006 Jetta BRM - Cold starts well and idles good until after a few minutes begins to miss or run terrible

[ihredneck]

It's worth mentioning i have viewed many (but not all) of bad/rough idle threads and have not found a solution.

2006 Jetta BRM - 5 speed with 297k miles, no CEL's and VCDS autoscan is clean too.
This only occurs after starting the car while it's been sitting for some time (sitting on a flat surface) in warm/hot or cold weather.
The car starts right up after the glow plugs cycle, there is a decent amount of smoke (white/grey/blue) smells like cold start fumes on my ALH and Cummins. The smoke will clear up after a minute or so and the car idles just fine. After a few minutes it begins to ever so slightly run rough and progresses until it's obvious it is missing. If I raise the RPM up to 1500-2000 it's smooths out and if I leave it at that RPM long enough the rough idle goes away for good until the next cold start.
If I leave the car running at the bad idle, eventually a cylinder 4 misfire will show up on VCDS. I can see that IQ for injector 4 is quite high ~3 compared to the others hanging closer to -1 to 1. After running the higher RPM, the IQ of injector 4 drops into line with the other 3 injectors.

A few items I've done that haven't made a difference:

• New tandem pump (replaced just before i got the car due to a no start, was not the reason for no start)
• New fuel filter
• New air filter
• Replaced alternator clutch pulley (it needed it)
• Rechecked timing with timing tools
• Set torsion to 3.7
• Ran car with MAF unplugged
• Replaced MAF sensor (preventative maintenance)
• Installed new lift pump (flow was getting low)
• replaced crank sensor (it had failed)
• Adjusted turbo actuator variance to 150

Any thoughts would be helpful. If it was injector seals, injector, injector lash, injector harness or cylinder compression I would have expected it to be at startup too.
I may run do a can's worth of diesel purge to see if that makes a difference and also set torsion a tad higher, maybe closer to 4.7.

Thanks for thinking about this with me.

 

[Mozambiquer]

It's worth mentioning i have viewed many (but not all) of bad/rough idle threads and have not found a solution.

2006 Jetta BRM - 5 speed with 297k miles, no CEL's and VCDS autoscan is clean too.
This only occurs after starting the car while it's been sitting for some time (sitting on a flat surface) in warm/hot or cold weather.
The car starts right up after the glow plugs cycle, there is a decent amount of smoke (white/grey/blue) smells like cold start fumes on my ALH and Cummins. The smoke will clear up after a minute or so and the car idles just fine. After a few minutes it begins to ever so slightly run rough and progresses until it's obvious it is missing. If I raise the RPM up to 1500-2000 it's smooths out and if I leave it at that RPM long enough the rough idle goes away for good until the next cold start.
If I leave the car running at the bad idle, eventually a cylinder 4 misfire will show up on VCDS. I can see that IQ for injector 4 is quite high ~3 compared to the others hanging closer to -1 to 1. After running the higher RPM, the IQ of injector 4 drops into line with the other 3 injectors.

A few items I've done that haven't made a difference:

• New tandem pump (replaced just before i got the car due to a no start, was not the reason for no start)
• New fuel filter
• New air filter
• Replaced alternator clutch pulley (it needed it)
• Rechecked timing with timing tools
• Set torsion to 3.7
• Ran car with MAF unplugged
• Replaced MAF sensor (preventative maintenance)
• Installed new lift pump (flow was getting low)
• replaced crank sensor (it had failed)
• Adjusted turbo actuator variance to 150

Any thoughts would be helpful. If it was injector seals, injector, injector lash, injector harness or cylinder compression I would have expected it to be at startup too.
I may run do a can's worth of diesel purge to see if that makes a difference and also set torsion a tad higher, maybe closer to 4.7.

Thanks for thinking about this with me.

Check the camshaft. That's the most likely cause of all that. Very common issue.

 

[ihredneck]

I will do a double check. I had done a cursory check when I had the cover off and looked for signs if lobe wear (sharp edges) and what I could see of the tops of the lifters.
So I will check cylinder 4 closely since that appears to be my problem area.

I can't seem to make sense of why it wouldn't run rough at startup but then get worse and then resolve after a bit. Do you mind explaining?

 

[ihredneck]

Why would any of those things (air filter,etc etc) only affect injector #4, and did you consider replacing/swapping #4?

Good question. I did several of those things prior to digging VCDS out and getting a CEL for a misfire. Most of it was due to be replaced.

I had considered but don't have new seals in hand and would need to order some.

 

[oilhammer]

Sounds exactly like a textbook bad injector to me. That's exactly what PDs do when the injector dies. They're OK when cold, and as they warm up they drop off, and once the ECU sees the misfire and has maxed out its fuel balance, it shuts the fuel off completely for that cylinder.

 

[ihredneck]

Sounds exactly like a textbook bad injector to me. That's exactly what PDs do when the injector dies. They're OK when cold, and as they warm up they drop off, and once the ECU sees the misfire and has maxed out its fuel balance, it shuts the fuel off completely for that cylinder.

Maybe it's because the injector is starting to fail, but I don't see why it comes back online and run out well after some engine run time.

 

[oilhammer]

It is because of thermal expansion/contraction. You can certainly try some fuel system cleaner, or if you have time to spend you can move the #4 injector to another cylinder and see if it follows.

BRM injectors are still available. They are unfortunately not cheap. But they are far less than some other PD injectors.

 

[ihredneck]

It is because of thermal expansion/contraction. You can certainly try some fuel system cleaner, or if you have time to spend you can move the #4 injector to another cylinder and see if it follows.

BRM injectors are still available. They are unfortunately not cheap. But they are far less than some other PD injectors.

Thanks for explaining it. It is helpful to have some of the understanding when troubleshooting to determine which steps I'll do first.
It may take a bit, but will follow up with what I find out.

Is it problematic to replace only 1 injector vs the whole set for a PD?

 

[Rx7145]

Someone awhile ago recommended this eBay seller for injectors. It’s in German and hard to read. Good luck.

Security Measure

www.ebay.com

 

[travelfreak]

Please run minimum quantity iq deviation adaptation. It will tell which injector is going to fail. Just replace that. I faced similar problem with my 1.6 polo sedan/vento(CLNA).

 

[325_Guy]

BRM injectors are still available. They are unfortunately not cheap. But they are far less than some other PD injectors.

Sidenote here, would you recommend that someone interested in taking a BRM to 500k+ bank a set of injectors for future repair purposes?

 

[ihredneck]

Sounds exactly like a textbook bad injector to me. That's exactly what PDs do when the injector dies. They're OK when cold, and as they warm up they drop off, and once the ECU sees the misfire and has maxed out its fuel balance, it shuts the fuel off completely for that cylinder.

Oilhammer, you nailed it.

The cause was a bad #4 injector. Got it replaced with another unit (new seals and TTY bolts) and there is no miss in that range from initial idle to warmed up.

 

[oilhammer]

Glad you got it fixed, and thanks for reporting back!