ALH Idle Misfire: Causes and Solutions

Hello everyone,
Unfortunately, I haven't found anything suitable for my topic in the search results.

My 2001 New Beetle TDI with an ALH engine and 186,000 km is giving me trouble with the cold start idle. The idle speed fluctuates between 850-1100 RPM. Initial 'rough' measurements with VAG-Com haven't revealed any abnormalities (all measured values are within the tolerance range, except perhaps the MAF sensor, which is providing correspondingly high values during engine speed increase).

What's interesting here are the settings of the glow plugs:

Idle: 10110000
When accelerating (from approximately 2,500 RPM): 11010000

After a few minutes, the glow plug indicator displays '11111111', indicating that the glow plugs have turned off. After that, the engine idles very smoothly. Acceleration and driving behavior are then completely normal.

My assumption is therefore that the afterglow could be the cause of the misfires and idle fluctuations.

Besides that, I've also noticed that the engine is producing a bit more smoke, but that could also be related to the mileage.

Does anyone have any suggestions as to what it might be, or any advice on how to proceed using VAG-Com (licensed full version)? Further data can be provided if needed.

Thank you very much.
Thomas.

Hi,

Check the coolant temperature reading in the engine control unit using VAG-COM by accessing the measurement blocks.

Best regards, Rainer.

The cooling water temperature is fine; it is continuously increasing from an initial temperature of 15°C, which is the outside temperature.

silverbeetle.de wrote:

The cooling water temperature is fine; it is continuously increasing from an initial temperature of 15°C, which is the outside temperature.

Okay... without the jump starter? Be careful, the double sensor in the cylinder head has 2 sensors, one for the combination instrument and one for the engine control unit. By the way, these sensors are really junk; in my A3, this is the second one that has failed. Thankfully, now only the temperature gauge in the combination instrument is malfunctioning, which isn't a huge problem for me right now.

If the engine control unit (ECU) experiences a temporary high-resistance fault, you'll have an increased idle speed (the ECU thinks it's extremely cold) and it would also explain the issue with the glow plugs.

Please log measurement block 2 in the engine control unit when the car is acting up.

Best regards, Rainer.

silverbeetle.de wrote:

Of particular interest are the settings of the glow plugs: Idle: 10110000 When accelerating (from approximately 2,500 RPM): 11010000 After a few minutes, the glow plug indicator displays "11111111", with the note that the glow plugs are then switched off.

This is exactly as it should be. After startup, it glows for a certain period (10110000). Normally, this afterglow is turned off after a certain time (11111111).

If the engine speed is still above 2500 RPM during the afterglow phase, the afterglow process will be interrupted (11010000).

Have you checked the spark plugs individually to see if they are still working properly?

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

Okay, I logged block 2 again tonight, and there were no anomalies. The temperature is continuously increasing from the outside temperature without any further jumps.

What I noticed about Block 13 is that the value for the second cylinder during the cold start phase is around 1.2 - 1.5 g/h (a quite significant deviation from the other cylinders, but it returns to a 'normal' (much lower) value once the engine is warm).

A table with the measurement values can be provided upon request.