AJM: Causes of Engine Jerking/Hesitation

Hello,

'After the machine (225,000 km) ran smoothly all summer, it's now experiencing issues again with temperatures below 10 degrees Celsius. It's shaking, mainly under full load and with a cold engine (with a warm engine, it only shakes slightly). I've already replaced all the filters and the oil. In what order would you suggest I investigate further, especially considering that it seems to be somewhat temperature-dependent?'

LMM (rebuilt approximately 20,000 units ago).
'Difficult-to-operate VTG (how to check?)'
LLK (how to check?)
Needle injector (how to test?).
Leaky hoses in the air circulation system.
Piezo injectors (can wear and tear manifest as engine misfires?)

What other possibilities do you think are worth considering, and which ones won't leave any traces in the error memory? In what order should I proceed with further checks, i.e., where is the highest probability of finding a fault?

'Needle insertion device for PD? Did I miss something?'

You can find a lot of information on the topic of 'how to' here in the relevant articles and information sections. Don't hesitate to use the forum's search function!

Also, your error description is quite vague. If you want to receive helpful answers, please provide more details, such as the speed range at which the problem occurs.

What about the AGR? Is it already closed?

Okay, so the machine doesn't have a needle lift injector. That eliminates one potential cause. I also just found this listed as a common cause of TDI engine misfires on tdi-ruckeln.de.

The search function is helpful for the keywords mentioned, but it doesn't provide the best order of action for the specific case. As I mentioned before, the problem mainly manifests at high RPMs (greater than 3600) and with a cold engine.

So, what would you do next?

You've listed potential candidates. You can find out how to verify this information using the search function. Here's how I would proceed: First, I would check everything you've described.

To me, this smells like a problem with the fuel supply, possibly also a PDE (throttle position sensor) issue.

Hi,

Just a moment... 3600 RPM and a cold engine? And: Full load and a cold engine?

Even if this doesn't help you with your "problem," it should be noted that both combinations are not good for your engine; quite the opposite!

Best regards,

Jan.

I'm also surprised that the engine lasts for 225,000 km for you. I get over 2,500 RPM on my AJM, even when it's cold, which makes me sweat. No, I won't do that to my 'little' PD engine.

Regarding your problem, it would be interesting to check if the temperature sensor is working correctly. There can be many causes for this issue. However, it's not a typical problem specific to the AJM model.

Perhaps you should check the car's error memory. Maybe you'll get lucky and find something recorded there.

Regards,
Frank.

Hello,

What does measurement block 13 (idle speed control) indicate?
Please note: engine must be warm (85°C or higher).

@Jan6K: 'Cold engine' is of course relative; for me, it means that it vibrates more during the first 100 kilometers than during the last 100 kilometers, which suggests a temperature dependency. It's obvious that you shouldn't immediately rev the engine to 3600 RPM from a standstill.

@frank_24: No need to panic, I'm confident the machine will keep running. Your comment about a temperature sensor is interesting: Are you referring to the coolant sensor? It's been faulty for a while, but I thought it only affected the coolant temperature gauge. Does it also influence the engine management? I'll definitely replace it. Or are you referring to a different temperature sensor?

@Michael II: The idle speed control was fine 2 months ago. I can't measure it myself yet, but a friend will do it. But if things continue like this, I'll probably have to bring my laptop with me to the car soon, for these very specific problems. But what does the idle speed control have to do with the jerking at high RPMs?

Best regards,
Ralf.

There are several temperature sensors on your engine, such as:

- Coolant (for combination unit)
- Coolant (for engine control)
- Intake air temperature
- Fuel temperature

The latter one had already annoyed me. However, it caused performance issues that were more temperature-dependent, rather than causing stuttering.

joergs wrote:

To me, this smells like a problem with the fuel supply.

I think so too.

Air leaks can cause PDs to stutter, and for example, can be temperature-dependent due to cracks in plastic parts, because the engine heat spreads through the fuel circulating in the system to the entire fuel system .