Rough Idle 1Z: Causes and Solutions

Hello everyone!

First of all, a huge thank you to this forum! I'm new here and already have a problem.

My 1Z engine is very loud and rough when idling. It's installed in a Volkswagen Passat 35i B4, manufactured in 1995.
The engine speed is very consistent at 1940 RPM (read with VAG COM). I've adjusted it to a lower value before, but then the engine runs even rougher.

He has no other problems, and the speed doesn't fluctuate.

The only issue he's experiencing is a slight hesitation during acceleration in 5th gear, between 1500 and 1900 RPM. It seems to be slightly worse depending on the outside temperature (and has been happening for about 50,000 km, without changing). However, I don't think it's related to the problem.

The vehicle doesn't produce any smoke and has its full power.

The only thing that bothers me is this 'rough' idling sound. It's gotten to the point where something inside the center muffler has come loose due to the vibrations and rattles around (but it's not catalytic converter parts, it's the muffler itself).

I recently heard a 110hp TDI engine (same year and vehicle model) from a friend, and even when it was cold, the idling noise was significantly quieter than mine is when it's warm.

Leaks in the exhaust system and intake manifold have already been checked. These issues can be ruled out.


Maybe someone here has some advice?

Hi,

You probably mean 940 RPM as the idle speed.
What is the difference between the setpoint and the actual value for the start of the injection process?

Best regards, Rainer.

Of course, 940 Umin!!!

Unfortunately, I can't say anything about the target value and actual value. (This is my first TDI, and I haven't dealt with this technology before; I'm just a gasoline engine enthusiast.)

Could this problem be related to a misaligned timing?

But I think that he would also experience a decrease in performance?

He doesn't! It runs like a dream! (It doesn't consume much fuel, but it can go downhill at 200 km/h without producing any black smoke.)

Maybe you know someone who had the same problem and was able to fix it?

Are you looking for a workshop that can help you, or do you want to check the target and actual values of the injection start?

Best regards, Rainer.

If this is related to the error, can I correct the timing (manually) and will that fix it? Or do I need to adjust it using VAG Com with a laptop?

Is this purely a mechanical issue, or is it electrical?

But don't you think that an error in this area might have other consequences?
Sure, here is the translation of the text from German to English:

'For example, poor starting or loss of power?'

4-Runner wrote:

If this is related to the error, can I correct the valve timing (manually) and will it then be gone??? Or do I have to adjust it with VAG Com using a laptop??? Is this a purely mechanical thing? Or is it electrical?

The start of injection molding is an "electromechanical" phenomenon (for newcomers).
The configuration should be performed using a diagnostic device (e.g., a laptop).

Further explanations only make sense once you understand the principle.
Okay, I'm ready. Please provide the German text you want me to translate into English. Just paste it here, and I will give you the translation.

Sure, thanks in advance!

After reading the article at the link, I think the error is related to that.

That's likely also causing the slight jerking during partial load operation. When you give it full throttle in fifth gear, there's no jerking.

I assume that during the last timing belt replacement (which was done at an independent workshop), the valve timing wasn't set perfectly.

The workshop probably won't even have a diagnostic tool.
The previous owner hadn't taken the TDI to a VAG workshop for ages.

I'll be replacing the timing belt and adjusting the valve timing sometime in the next few weeks.

I'll post again later to see if it made a difference.

Regards...

Hello!!
I'm having the exact same problem!
Is it already resolved?

Best regards,

Eric.

Hello fellow sufferers,
I also had the problem with the rough idle. In desperation, I had already increased the idle speed, but that didn't solve anything. I struggled with this issue for about 2 years until I finally got an error code in the diagnostic system: Error 1242 - Output stage in the control unit, interruption/short circuit to positive.
I measured the continuity of each wire between the control unit connector and the connectors for the individual components, and also checked for variable resistance (if the value changes when moving the cable, there's a problem).
I found the problem with the LMM; the brown and white wire (sensor mass) was faulty.
I quickly soldered on a different plug.
Now the hesitation when starting has also disappeared, and the engine is running smoothly again.
I hope that this can help some people who are going through a similar experience.

Best regards from Heide, and always have a smooth flight.

Benno.

Benno wrote:

I measured the individual wires between the control unit connector and the connectors for each component to check for continuity and variable resistance (if the value changes when moving the cable, something is wrong). I found the problem with the LMM; the brown and white wire (sensor mass) was faulty. I quickly soldered on a different plug.

Um... which plug is the new one now?
It's connected to the LMM, or something that's a large part of the engine computer.

Hello Ulf,
The issue was with the connector at the mass airflow sensor (MAF). There was a loose connection, whether due to a broken wire or a poor crimp. I don't have the right tool to remove those small pins, so I couldn't just solder it. However, I had an old wiring harness lying around; that's why I took such a drastic approach.

Regards,
Benno.

Is it already solved?

Unfortunately not yet, I haven't had the time to look into it. But I have a feeling that it sometimes runs quieter and sometimes louder.

It sounds like a slow-moving Golf Mk1 with the hood open and rattling heat shields.

Right now, the thermostat is also broken, and I'm freezing my butt off in the mornings.
I think this should be our top priority because winter is just around the corner.

I'll get back to you when I have more information about the issue with the rough running.

DEFECTIVE thermostat???

Well then, you shouldn't be surprised if it doesn't work as expected.

The temperature is not only measured for display purposes; it also plays a role in various control and regulation processes within the engine's computer system.

And if the engine is kept at a "frozen" temperature (or it actually is), then the fuel will be injected differently...

First, fix all known errors, then you can tackle the unknown ones, and if necessary, create new ones (if it's boring).

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

The thermostat has only recently become defective.

I've been dealing with that other problem for ages.

Hmm, okay... so they probably don't have anything directly to do with each other - but that could be - we've been here before.

How does the volume change?

Could there be a blockage in the spray nozzle?

You don't have an interface and VAGCOM? That's a shame, otherwise I would have suggested a "basic setting" in group... hmm, I think it's 4..

The injection molding machine is running at full speed in both directions, which can be seen from the readings of the NHG (presumably a sensor or measurement device) and heard from the noise it's making.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

I have the exact same issue... seeing 'Topic: Nail/Knock' and '1Z TDI'.
'My performance depends on the outside temperature. Also, the 'loudness' and how long it takes to warm up are very slow for my 1Z; it probably takes about 10 km of city driving before it reaches 80 degrees Celsius. Are there any new developments? I'm going to check the connector for the mass airflow sensor. I've also been advised to tap into the ground wire and connect it to a grounding point on the chassis.'
Better quality mass airflow sensors result in slower wear and tear/degradation.

Best regards,
Eric