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OnlineMechanic
OnlineMechanic, Mechanic
Category: Audi
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Experience:  3 years Autozone Manager, 10 years Mechanic
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Engine miss fires at low revs when warm

Resolved Question:

Engine miss fires at low revs when warm. Absolutely no problem when cold. Had fuel filter/plugs changed recently
Submitted: 6 years ago.
Category: Audi
Expert:  OnlineMechanic replied 6 years ago.

Hello and thank you for choosing Just Answer.

 

Did the check engine light come on?

 

 

Customer: replied 6 years ago.
No lights came on
Expert:  OnlineMechanic replied 6 years ago.

Does the light flash when it's at low RPMs?

 

 

Customer: replied 6 years ago.
No
Expert:  OnlineMechanic replied 6 years ago.

Thank you.

 

So other than the low rpm issue, do you have any issues with acceleration or high speeds?

 

 

Customer: replied 6 years ago.
Its very rough (jerky) when accelerating up to about 2,500 RPM once warm but past taht its fine. Cruising is fine also. It seems to be when the engine is at idle or when it is under strain. I was thinking it has something to to with the ignition set up (coils, leads etc) or the temp/O2 sensors but I'm no expert hence me asking you guys!

Thanks
Expert:  OnlineMechanic replied 6 years ago.

Thank you.

The possibilities that you listed usually trigger a check engine light to come on. I am surprised that it has not come on yet.

 

To me it sounds like the Idle Air Control Valve (IACV) is not allow air to by pass into the chambers which is causing a misfire.

Remove the IACV and spray it down with carb cleaner. Then wipe it using a clean cloth. Put the valve back and see if this improves the issue. If there is a change in the operation, however it does not solve the issue, the valve may need to be replaced.

The valve is mounted on the throttle body and looks like this:

 

image

Also check if there is any wear/damage where the arrow is pointing on the picture.

Customer: replied 6 years ago.
If this doesn't solve the issue, what are the other options?
Expert:  OnlineMechanic replied 6 years ago.

We would have to check the spark plug gaps (since they got changed recently). We would also have to clean/test the mass air flow sensor and possibly do a spark test to see if the plugs are firing correctly up to specs.

 

 

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