Engine Misfire at Low RPM: Troubleshooting Guide

When I'm driving my car, and I'm in gear and approaching a traffic light, and the engine speed goes from 1200-900 RPM, my car vibrates or jerks slightly! You can feel it in the gear stick and in your 'butt'!

The same thing happens when the engine is idling, and even when I briefly accelerate it to 2000 RPM, the revs drop! While idling, I can also hear a slight metallic rattling sound in that range.

I'm at my wit's end! Everything is stuck in the engine compartment, but otherwise, the engine runs perfectly!

It's a 1996 Audi A4 with a chip tuning modification and 214,000 km (approximately 133,000 miles) on the odometer.

I recently had the clutch replaced, but that probably has nothing to do with it, right?

Maybe you can help me!

Best regards and thank you.

Manuel.

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

'Addendum:'

I just figured out, with my wife's help, that this rattling noise is loudest at exactly 1000 RPM and it's coming from the lighting system!

I'm now suspecting that the alternator is faulty, based on the premature wear of the V-belt.

But can the alternator, via the serpentine belt, have such an influence on the engine?

Thank you.

Manuel.

Hi Manuel,

If you had used the search function, you would have found the article by Ulf about the point machine. At the end of that article, it mentions a tendency for jolting. The opposite effect suppresses this jolting.

I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

The second article addresses exactly the problem you're facing.

Okay, I'm ready. Please provide the German text you want me to translate.

I did read that!

It's hard to explain, it's not really a jolt, more like small vibrations!

Since this issue has only appeared in the last approximately 3,000 kilometers, and my alternator is making noises that are almost as loud as the engine, I think the problem is likely related to the alternator.

Background:

In 2001, I took my car to an authorized Audi service center to have the water pump replaced, and when I got the car back, a blade on the viscous fan was broken!

Of course, I wasn't told this, and the mechanic probably didn't dare to report the damage he caused, nor did he install the €20 replacement part.

Less than 10,000 km later, the car was back in the workshop because the imbalance of the viscous coupling had caused all the bearings driven by the ribbed belt to fail!

Everything was renewed, except for the generator, as it was still considered to be in good condition at the time!

Therefore, I'd like to reiterate my question: Can a faulty alternator bearing have an impact on the engine?

Regards,

Manuel.

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Hi Manuel,

Manuel Thomas wrote:

Everything was renewed, except for the dynamo, because it was still considered to be in good condition at the time! Therefore, I'd like to reiterate my question: Can a faulty alternator bearing have an impact on the engine?

Since every amount of resistance puts a strain on the motor, even a faulty alternator can cause jerking. However, you should definitely notice it if the alternator's freewheel mechanism is not working properly.

I just remembered something else:
"With my first rally car, after replacing the clutch, I experienced about 500 km (on the road, not in competition) of unexplained jerking. The clutch had completely failed. Subsequently, the KW bolts came loose, and the clutch disc was crushed. It was a manufacturing error. I hope that's not what's happening to you."

Okay, I'm going to replace the alternator now! I'm getting one from a salvage yard with a one-year warranty and 100,000 km mileage for €100!

Even if that wasn't the problem, at least I'm rid of that annoying running noise! And I can finally enjoy the sound of my car's engine again, instead of that annoying and embarrassing scraping sound!

However, you should definitely feel that with a free-range Lima bean!

According to E**, I also have a free-running pulley! Could you please explain that to me briefly?

Jerking. According to my definition, jerking occurs when smooth driving in this RPM range is no longer possible!

That's not the case, it's more like a slight vibration! My wife doesn't even notice it, but I, well, I have a very sensitive 'butt meter'!

Regards,

Manuel.

Manuel Thomas wrote:

Jerking. According to my definition, jerking occurs when smooth driving in this RPM range is no longer possible!

Agreement. That's how I would also define "stuttering" or "jerky movement."


When I say "free-running alternator," I mean: remove the belt, manually rotate the pulley (in the direction of rotation), and assess the smoothness of the rotation. Normally, the alternator should rotate freely without any noticeable jerking or resistance.
However, if there's an electrical fault in the alternator that's causing the jerking, you obviously can't diagnose that this way.

I won't be able to check that until tomorrow!

But I would also like to commend the engineers.

Thanks for letting me disassemble half the car to change the headlights!

Vehicle front in service position
Loosen the V-belt.
Remove the viscous fan.
Replacing the alternator.

Okay, I guess I'll have to take it to a professional, since I can't remove the front panel myself!

Regards,

Manuel.