TDCI: Implausible Signals from Throttle Position Sensor

Hello everyone,

After a long absence, I'm posting here again, and unfortunately, it's not about a VAG vehicle. However, I can't find any PSA-specific forums online with people as knowledgeable as those here!

"Of course, VAG-COM/VCDS doesn't work with the TDCI engine, but I was able to get an OBD2 dongle to read data via my smartphone."

The engine stutters during partial load operation, around the point where the load changes, and it feels like an EGR valve issue, but it's more irregular. The cruise control engages and disengages every second or so on a slightly downhill road, and it seems to be regulating specifically around the point where you can trigger the stutter with the accelerator pedal.
Sometimes he doesn't do that.

So, I read out the parameters that are related to the intake system up to the exhaust manifold, including things like pedal position, air mass, boost pressure, and throttle valve.

Und dabei fiel mir das Signal vom Drosselklappensensor auf. Ich habe dann nach einem Kaltstart mal Gaspedalstellung und DK-Stellung geloggt, und man sieht, dass die DK-Stellung erst mal halbwegs plausibel aussieht, aber schon zunehmend mit Sprüngen und Aussetzern, und nach wenigen Minuten scheint sie fast nur mehr "fast geschlossen" (9,42%) zu "melden". Das ist der Wert im Leerlauf. Ob die Leerlaufdrehzahl via Klappe oder LLR gehalten wird, weiß ich leider nicht, mangels Wissen ob da ein LLR verbaut ist, man sieht auch schlecht hinten rein, wo der Krümmer, Turbo usw. sitzt (Motor: AH01 2,0 BlueHDI). DHowever, the value is the same at every idle speed.

I suspect a contact problem (ground connection, sensor cable, or connector) that seems to be temperature-dependent. The effect was more pronounced at temperatures below -10°C than it is currently, with temperatures just around freezing.

Please share your valuable opinions on this.


Thank you, and I'm sorry for intruding with a non-VAG problem .

Hi.

Quote:

VAG-COM/VCDS naturally doesn't work with a TDCI engine,

Yes, VCDS can do that via the OBD2 button , but the RKS+CAN interface can even do more via the OBD2 connection.

Quote:

Whether the idle speed is maintained by the throttle valve or the load control lever (LLR)

No, the flap is used to better adjust the EGR airflow. It also helps with a smoother engine shutdown. The idle speed control has nothing to do with it.

The engine control unit (ECU) simply adjusts the fuel injection amount to maintain the idle speed.

I would check all the lines leading to the EGR valve actuators, the throttle body, and the mass airflow sensor for any loose connections or signs of damage caused by rodents.
If the actuators themselves have mechanically worn components or if the position feedback system simply doesn't work reliably, that could also be the cause.

Sure, here is the translation of the text from German to English:

"LG" translates to "Best regards" or "Sincerely" in English. It is a common abbreviation used at the end of emails and letters.

Hey Boss .

I've added another dataset with AGR rate and air mass, and the throttle values appear reasonably plausible if we assume that 100% means "closed" and 0% means "fully open." The valve briefly closes to help the engine draw in the volume of air from the exhaust stream (so to speak). During cold start, the throttle seems to force a higher recirculation rate, presumably to warm up the engine faster.
After reviewing the values, and noting that the curve of the flap sensor closely follows that of the valve control system, I was able to rule out the DK sensor as a major source of error. However, there are some discrepancies: for example, when the control signal is at 88%, the sensor reports approximately 70%, and when the control signal is at 0%, it reports 9.41%.
Either the valve wasn't calibrated, which, according to the friendly technician, should happen automatically, or the "learning effect" isn't visible in the raw data, and the system "knows" that a DK position of 9.41% corresponds to a 0% opening, etc.
Another possible explanation would be a dirty valve that doesn't close completely and leaks.

Regarding the learning process, I followed the countless information available online, and indeed, if you press the accelerator pedal all the way down three times immediately after turning on the ignition, the DK valve motor starts to hum. However, it's a monotonous sound that doesn't change or stop for over 10 minutes, but only ceases after the next engine start.

I will continue searching for errors in the intake system, all the way to the EGR valve. Thank you for your tips and information so far, and I will be sure to report back with my findings.

Then I found an old Lexia3 in the basement, a relic from my brief foray into the world of Citroen cars. It apparently still works with the Vivaro and allows me to gain further insights, although I first need to free up a laptop for it.

Best regards,
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