A3 Engine BGU, Jerking/Unstable Idle

Hello!

Perhaps someone here can help me; there are a few oddities.
which I can't really assess.

The vehicle is an Audi A3, manufactured in 2003, with a gasoline engine, 1.6-liter displacement, and engine code BGU. It has 152,000 kilometers on the odometer.

The problem is that the engine sometimes runs roughly, with fluctuating idle speed, and the engine check light is illuminated in yellow.

Okay, logically the first step is to read out any error codes; it mentioned something about the AGR valve and the secondary air pump.

I took a quick look, and I found that 2 hoses were broken.
"The air intake duct, connecting the air filter box to the throttle body, had a small hole at the branch leading to the engine case ventilation system and cylinder head."
The engine crankcase ventilation hose was connected from the front center to the cylinder head.
completely.
Replaced the hoses, cleared the error codes, test drive, everything's fine.
How to do it without wasting money unnecessarily.

"Okay, I thought, done, everything's fine."

Unfortunately, that was the wrong approach; I ended up keeping the car running in neutral somehow.
Suddenly, while idling, the engine starts fluctuating in RPM.
So im 2-Sekundentakt immer so von 800- auf 900 und wieder zurück.
Then I turned off the engine, restarted it, and it ran smoothly for a few minutes at idle before starting to "sputter" again.

The throttle body didn't actually look excessively dirty; I could see that when I replaced the hose.
I wasn't brave enough to press them down to verschandeln them.

So, I got the laptop out and tried to adjust the throttle settings.
Not sure if that worked, basic settings, then block 60, start or OK.
then it was on the right side, throttle valve adjusted, input/output OK.

Okay, so I've gone through everything again, roughly.
So, the engine control light is still off, and the error memory is empty.

The engine was running at idle and was so hot that the radiator fan was turning on and off.

The coolant temperature was around 76-81° .
"Intake manifold pressure is 326 mbar. I'm unable to determine what's happening with the throttle valve in this gasoline engine based on that reading. Is that a plausible situation?"

Then, the lambda sensor:
Intrinsic value: 1.69
Set point: 0.99
Probe voltage B 1 S 1: 2.89 V, as measured.
Probe voltage B 1 S 2: 0.12 V, no change.

The exhaust fumes smelled toxic, and a little bit of condensation was dripping from the exhaust pipe, but not much.

I'm not quite sure what to say now.
Could it be that the temperature sensor is giving incorrect readings?
and therefore the lambda regulations are not active.
or something like that?

Unfortunately, I only realized too late that I should have used a pyrometer to measure the actual engine temperature, but I will do that eventually.
The temperature gauge on the dashboard is showing a normal reading, but as always, you can't really rely on it completely.

Quote:

Leider bin ich erst zu spät auf die Idee gekommen, mal mit einem Pyrometer die tatsächliche Motortemperatur zu messen, aber das werde ich noch machen.

"When the electric fan kicks in, the temperature should be around 95 degrees. What does the intake air temperature reading show?"
When cooled down, both sensors should display approximately the same outdoor air temperature.

Assuming the engine is over-oiled:
Does the oxygen sensor react when you introduce unmetered air into the engine?
Possibly check the lambda sensor voltage with a multimeter.

Starting from measurement block 086 and onwards (including Ready bits, cycle bits, and error bits), search for errors.

Cleaning the throttle body would likely be a good idea at 150,000 kilometers.

Hi!

Sure, I completely forgot about the intake air temperature.
That was 33 degrees Celsius (91 degrees Fahrenheit) with an air temperature of around 5 degrees Celsius (41 degrees Fahrenheit). It's actually almost unbelievable, but the engine was hot, and the intake manifold was also warm to the touch.

I wasn't brave enough to verschandeln the throttle body myself. Can I just pry it open? (It's electronically controlled, after all.)
to get rid of the grime/dirt.

Oxygen sensor: So, I didn't introduce any vacuum leaks, but when I briefly accelerated to full throttle, the readings didn't change at all.

I can't make any sense of anything related to the MWB 86 or later versions.
"I'll take a closer look at this and search the forum; maybe I can figure it out. I just have a small problem, being someone who didn't grow up speaking English, that I don't understand English FAQs as quickly as most people do. It's always a bit of a hassle..."

Otherwise, thank you for your reply.
I'm not stressed about it either, because he's working abroad somewhere, and I can easily keep the car there for a week. That way, I can thoroughly check everything at my leisure.

And also, it's kind of strange that so many things are weird here all at once.
Are there any known issues or experiences where ground connections are problematic?
"...so that everything somehow connects and works together? For the engine control system?"
I hadn't even thought of that yet .

Hi there,
Please copy the error messages and measurement block sections here exactly as they are; this will make searching easier.
If the problem with the secondary air pump wasn't caused by a connector that was disconnected during maintenance, then it still exists and will reappear in the system memory. The faulty hoses are likely not related to this issue.
To assess the probe voltages, one would first need to know the types of probes being used. The probe labeled "Kat" is certainly a jump probe, but I'm not sure about the type before "Kat."
Are the values from the temperature sensors plausible?
hg
Herbert.

Hi!

I had a brief opportunity today to take another look at the car.
Okay, the yellow warning light is on, the engine is off, and there's a stored error code indicating a malfunction with the EGR system.
Here's the translation:

"This includes, among other things, environmental conditions and a voltage of 12.2V."
The problem with the secondary air pump hasn't reappeared, which I already knew because the pressure was being released through the defective motor housing vent.


The coolant temperature today was plausible, according to the individual measurement and the reading taken with a pyrometer on the water hose. It was around 90°C, which seems accurate.

But something about the electrical system doesn't seem right.
Then I checked the voltage in the engine control unit again, specifically regarding the voltage regulation (AVR).
very interesting:

If the engine idles smoothly and shows a voltage of around 14.24V, that's perfectly normal.
When the engine then experiences a misfire, the idle speed drops by about 200 rpm and the voltage drops to around 12V.
I also noticed today that the interior light in the car is flickering almost in sync with it.

I think I'm going to take some time to carefully examine the basic electrical system, checking all the cables and ground points from the alternator (Lima) to the battery. Maybe I'll even create a few temporary grounding connections for testing.

Are there any experiences available that I should look for first?

Quote:

Gibt es da vielleicht Erfahrungen, wo ich am ersten suchen sollte?

Right where it's easiest to access -- at the battery.

Steffen G wrote:

Hi! I wasn't brave enough to verschandeln the throttle body myself. Can I just pry it open like that? (It's electronically controlled, after all.) to get rid of the grime/dirt. Oxygen sensor: So, I didn't introduce any vacuum leaks, but when I briefly accelerated to full throttle, the readings didn't change at all.

Hi Steffen! You can safely press the throttle valve open with your hand. Cleaning it helps a lot on this 1.6L engine, but don't forget to reset the adaptation afterwards. This should make the engine run more stably at idle. Unfortunately, you won't be able to eliminate it completely; +/- 50 RPM fluctuation is perfectly normal.

The oxygen sensor BEFORE the catalytic converter MUST fluctuate, just like when measuring gas levels. The oxygen sensor AFTER the catalytic converter should not fluctuate much at all; this sensor checks the effectiveness of the catalytic converter.

Also, like a car service would, also check this! Keep in mind that at certain low engine speeds, the alternator hardly charges - the voltage drops significantly, especially when the air conditioning is on or the lights are turned on. This is particularly noticeable with an aging/not properly charged battery.