Sporadic Empty Runs AJM Automatic

Passat 3B5, year 2000, AJM, Automatic, 85,000 KM

Error Description:

When the vehicle is stationary and the gear is in "Park" or "Neutral", the idle speed fluctuates sporadically for a very short period (approximately 0.5 seconds) to around 1000-1100 RPM, then returns to the normal range in intervals of approximately 10-20 seconds. Emotionally, I would say that the engine speed, before it increases, actually decreases slightly (barely perceptible), similar to a brief interruption.

All error codes are cleared. I suspect the temperature sensor. Unfortunately, the vehicle was already at 65°C during the diagnosis. The corresponding measurements were plausible. After test drive and reaching normal operating temperature, the error was no longer reproducible.

Does anyone have any ideas?

Mhh, could it be that, especially when the engine speed momentarily drops, something is drawing power, and the higher load on the alternator then causes the idle speed to increase?

Quote:

Hmm, is it possible that, especially when the engine speed briefly drops, something is drawing power, and the increased load on the alternator then causes the idle speed to increase??

Possible, but what? I've turned off everything that I could. Voltage is constant at 14V. I will check it again.

Quote:

Possible, but what?

Solution: Herzog's LMM. Unbelievable what kind of errors these things can produce.

Why I haven't noticed this here: /viewtopic.php?t=12257&start=0&postdays=0&postorder=asc&highlight=herzog, is beyond my knowledge

Therefore - if there's nothing sensible on it, then there's nothing sensible in it.

Unfortunately, I couldn't get a Bosch LMM at that time (Saturday afternoon), otherwise, this probably wouldn't have happened.

So, don't touch this stuff!