TDI Passat: Idle Speed Control Explained

Hello,

I'm having some issues with my Bosch service center! They want to replace the turbocharger in my car (it sometimes has turbo lag), they're claiming a faulty thermostat when it's actually a broken display, and they keep trying to install a new throttle position sensor!

Regarding the issue:

I always get a different idle speed. Starting, stopping, etc., each time it fluctuates between 860 and 1300 RPM. The throttle position sensor has been replaced.
'It has already been replaced, but VAGCOM still shows values of 1.6% load at idle (at different altitudes!!!). I also logged a city driving session.'
If I keep my foot on the brake pedal while the car is stationary and give it two quick bursts of acceleration, the engine speed drops to the target value, but the engine speed gets stuck around 1000 RPM during the first burst of acceleration.

The workshop seems to doubt my understanding and apparently doesn't want to put in the effort to troubleshoot the problem.

I suspect there's an issue with the electrical system or the control unit, but I'm not able to diagnose it further with VAGCOM.

Has anyone else experienced similar problems?

And how can I use VAGCOM to correct the throttle position sensor to 0% load?


How can I publish the log file?

kubs wrote:

If I keep my foot on the brake pedal while the car is stationary and give it two quick bursts of throttle, the engine speed drops to the target value, but the engine speed gets stuck at around 1000 RPM during the first burst of throttle???

I'm just guessing here, but it seems like there might be mass-related issues = fluctuations / contact resistances. I think the ground connection in the footwell area probably connects the accelerator pedal sensor, the brake contact (and the clutch).

and be sure to check all the other connectors, including the connector on the EDC (Electronic Data Carrier).

Example 1: Jerking and interruptions at low temperatures. Cause: Worn-out contact springs in the airflow sensor.

Example 2: The engine is sputtering and struggling, seemingly on its last legs. After a lot of searching and component replacements (using parts from a donor vehicle), the Motronic control unit was finally examined. A large amount of water came out of the connector (even though it was located inside the vehicle and everything else was completely dry). After drying it out, the engine started running again.


CU Gremlin.

The engine runs smoothly otherwise! No coughing or sputtering!
Otherwise, I would hardly have an average fuel consumption of 5.6L. Sometimes, I can even achieve just over 4L on trips in the countryside. I just can't let the engine idle too often .



Here is the VAGCOM log:

http://www.35i-forum.de/forum/attachment.php?attachmentid=2383&sid=

You can only see the log if you are logged in to this forum .

m;

I have read the FAQ, but I still don't know where I can upload an attachment .

Broad question about my problem:

I have a cable connected to the control unit that appears to have a resistor attached to it, and the insulation seems to be poorly stripped. Is there a pinout diagram available for my control unit so I can figure out what it's for?

kubs wrote:

Is there a pinout diagram available anywhere for my control unit so that I can figure out the meaning of each pin?

What control unit are we talking about? What is the part number? Or is it an MSA12 or an MSA15? You can identify it by whether it has a completely metal housing or just a metal connector block with the rest being plastic.

And which PIN are we talking about?

If it concerns an MSA15, then here is some information from Rudi: http://www.chiptuningforum.com/phpbbchip/viewtopic.php?t=330&highlight=pinbelegung

Regards,
Guste.

Hi,

"Regular" users are not allowed to upload files; they can only embed them using a link or copy and paste the content directly into the post.

Best regards, Rainer.

Is there a similar option available for the MSA12 STG?

gerbi wrote:

Is there a similar option for the MSA12 control unit?

Guaranteed!

However, I haven't researched the older models, so I can't offer you a link. Just take a look at a corresponding wiring diagram; you should be able to assign functions to at least 90% of the pins. However, the information might not be very well documented. But perhaps you could compile that information? We'll also help you with the missing pin functions as best we can.

Regards,
Guste.