I feel your pain having gone through that last year. At least you have a warranty that might cover it.
Unfortunately I had to foot the bill for mine, and to add insult to injury had to waste a weekend unpaid fixing it!
Lumpy engine start and idle
- Thread starter shaiboyuk
- Start date
I feel your pain having gone through that last year. At least you have a warranty that might cover it.
Unfortunately I had to foot the bill for mine, and to add insult to injury had to waste a weekend unpaid fixing it!
Great news got van back yesterday, full fuel system replaced and seems good. Done about 50 miles with it yesterday and doing 100+ miles today, so fingers crossed.
Plugged VCDS and not showing any faults (touth hair wood....my head), will rescan later and hopefully do cold start log tomorrow for @mmi
Plugged VCDS and not showing any faults (touth hair wood....my head), will rescan later and hopefully do cold start log tomorrow for @mmi
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Think I may have spoken too soon....
Started van yesterday morning, and stated rough idling again ARGH but this time went away fairly quickly and not affecting drive.
Started again this morning, from cold and again rough idle DOUBLE ARGH. Thankfully for this start, I had VCDS ready and logging for @mmi to work his magic
Attached logs (in order of doing them):
TEST 3 LOG-01-IDE09327_&11-Start-From-Cold.CSV
TEST 3 LOG-01-IDE09327_&11-idle rev.CSV
TEST 2 LOG-01-IDE00083_&11-Start-already-started.CSV
Log-WV1ZZZ7HZKH185023-57710km-35859mi-after-257-miles-of-drive.txt
(Aware of faults in this log, they are separate issues)
blockmap-IGN-ON-ENG-OFF-01-04L-906-056-RJ_WV1ZZZ7HZKH185023-20250315-1010.CSV
blockmap-IDLE-01-04L-906-056-RJ_WV1ZZZ7HZKH185023-20250315-1013.CSV
Started van yesterday morning, and stated rough idling again ARGH but this time went away fairly quickly and not affecting drive.
Started again this morning, from cold and again rough idle DOUBLE ARGH. Thankfully for this start, I had VCDS ready and logging for @mmi to work his magic
Attached logs (in order of doing them):
TEST 3 LOG-01-IDE09327_&11-Start-From-Cold.CSV
TEST 3 LOG-01-IDE09327_&11-idle rev.CSV
TEST 2 LOG-01-IDE00083_&11-Start-already-started.CSV
Log-WV1ZZZ7HZKH185023-57710km-35859mi-after-257-miles-of-drive.txt
(Aware of faults in this log, they are separate issues)
blockmap-IGN-ON-ENG-OFF-01-04L-906-056-RJ_WV1ZZZ7HZKH185023-20250315-1010.CSV
blockmap-IDLE-01-04L-906-056-RJ_WV1ZZZ7HZKH185023-20250315-1013.CSV
Interesting.... 
Still seems to be the same/similar as in post #43 (2025-01-27 LOG-06) - at the startup "cylinder 4 internal moment" (calculated by ECU) lags compared with cylinders 1-3.
www.t6forum.com
Just a note: there was a small gap in the data stream thus missing samples between 2.33 and 12.11 seconds.
Not sure if the "statistics" below are anything useful/meaningful - at the moment. Obviously need to do comparisons with supposedly good engines...
Still seems to be the same/similar as in post #43 (2025-01-27 LOG-06) - at the startup "cylinder 4 internal moment" (calculated by ECU) lags compared with cylinders 1-3.
Lumpy engine start and idle
1.2 ° is ok then? Yes, actually even "better" than on mine having renewed the timing belt three months ago, and definitely not the culprit for lumpy running. Need to be cleaned or cleaner through it? or a different type of regen? Perhaps could try what a forced DPF regeneration while driving...
Just a note: there was a small gap in the data stream thus missing samples between 2.33 and 12.11 seconds.
Not sure if the "statistics" below are anything useful/meaningful - at the moment. Obviously need to do comparisons with supposedly good engines...
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Certainly would be nice (for me at least
) - to prove the "phenomena" can be reproduced.I'm afraid one can conclude much about MFD displays. The MFD smoothes out the extra fuel burnt by DPF regen in the following 40-70 miles by decreasing the shown MPG by some 15%. This affects similarly/drastically also to estimated remaining distance.
In the blockmap you were 44 km since last DPF regen so at that time the MFD definitely was showing poor figures.
Below a plot demonstrating the remaining range behaviour. Each dot was kilometers gained or lost on a 30 km journey. The zero means range display was in sync with driven distance - thus 30 km driven = 30 km loss in remaining range.
E.g. +80 kilometers below means I gained 80 kilometers in range by just driving 30 km
More:
[T6_measured] Fickle fuel consumption on MFD – encore
In March 2020 finally got the long-awaited ECU (Engine Control Unit) software update. Unfortunately it took a while to get a good chance to do some measurements to try to figure out what has been changed. So finally a few weeks back dusted the VCDS and collected all kind of intriguing data. The...
Certainly would be nice (for me at least
Your wish
Done another log this morning when starting. TEST-3-2025-03-16-LOG-01-IDE09327_&11-Start-From-Cold.CSV (attached)
After this log, I revved van and it seems to clear lumpiness. Could it be as simple as a glow plug in cyl 4 causing this? :/
yeh definitely know that MFD isn't the best. But for it to drop range from 70 miles to 30 miles in seconds didn't set right :/
I normally use Fuelly to track my mpg (Fuelly Link), but not wanting to put lots of fuel in van, as lost 60 litres last time it went in garage.
Where do I go from here, I know I need to go back to garage with it, but can't take another 7 weeks+ without it again.....
TEST-3-2025-03-16-LOG-01-IDE09327_&11-Start-From-Cold.CSV (attached)
Seems to be reproducible.
Doubt it. Should throw a fault. Also the glow plugs are ON about 120 seconds from startup.
(1) What are production dates of charge cooler and EGR cooler (stickers on the unit) - just wondering if they are the original ones or possibly replaced at some point?
(2) Any service/repair history of the vehicle?
(3) Did the garage do compression test?
(2) Any service/repair history of the vehicle?
(3) Did the garage do compression test?
Will be original as never been replaced. would EGR cause issues with single cylinder ?
I've had van from 1500 miles and been serviced every year
currently at 35k miles.
When spoke to manager today he said they done a compression test, and all cylinders were within tolerances. But believe it was done when engine had heated up, but this was normal. Rather than doing it when it was cold.... , said cylinder 4 was at 22 (bar?) which was the lowest of all cylinders but still within tolerances. He said it can go down to 19 before issue .....
May need them to do the compression test when engine is cold, to see variations between cylinders?
I've said that to them, they have said they have a set procedure for testing and that includes it being warm.... But are going to retest, and hopefully will leave it in garage the night before testing.......
Just out of interest I put your symptoms into chat GPT IA and this is what it told me:
A lumpy or rough idle on a cold start in a VW T6 (or any vehicle) can be caused by several potential issues. Here are some common ones:
I wonder how long it will be before AI will know more than MMI
A lumpy or rough idle on a cold start in a VW T6 (or any vehicle) can be caused by several potential issues. Here are some common ones:
- Dirty or Faulty Idle Air Control Valve (IACV): The IACV controls the amount of air bypassing the throttle body during idle. If it’s clogged or malfunctioning, it can cause uneven idling, especially when the engine is cold.
- Vacuum Leaks: Any leaks in the vacuum hoses can cause unmetered air to enter the engine, disrupting the air-fuel mixture. This can make the engine run rough at idle, particularly when it's cold and the engine management system is adjusting for higher idle speeds.
- Fuel Delivery Issues: A clogged fuel injector or a failing fuel pump can cause uneven fuel delivery, leading to rough idling. The cold start process requires a richer fuel mixture, so any irregularity in fuel flow could cause a rough idle until the engine warms up and the system compensates.
- Ignition System Problems: Worn or dirty spark plugs, faulty ignition coils, or a weak spark can cause misfires, leading to a lumpy idle. This is especially noticeable when the engine is cold and the spark plugs might not fire as efficiently.
- Temperature Sensor Malfunction: The engine’s coolant temperature sensor helps the ECU adjust the fuel-air mixture during cold starts. If this sensor is faulty, the engine might receive the wrong air-fuel mixture, causing rough idling.
- Air Intake or Throttle Body Issues: If the throttle body is dirty or the air intake system is clogged, it can cause a rough idle due to inconsistent airflow into the engine.
- EGR Valve Issues: A malfunctioning EGR (Exhaust Gas Recirculation) valve can affect the engine’s performance by allowing too much exhaust gas back into the intake, disrupting combustion, especially at idle.
- Low-Quality or Incorrect Fuel: Using poor-quality fuel or the wrong type of fuel for your engine can also cause rough idling, especially when cold.
- Engine Control Unit (ECU) Software Issues: In rare cases, the vehicle's ECU may need to be updated or reset to correct idle problems.
I wonder how long it will be before AI will know more than MMI
I think it's consistent with data gathered earlier. Although somewhat similar behaviour now briefly in cylinder 2 - which was not noticeable before. Perhaps just carried over from cylinder 4 (because of firing order 1-3-4-2).
Thanks for sharing
