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AudiDoc, ASE Certified Technician
Category: Audi
Satisfied Customers: 6456
Experience:  Independent European garage owner. Over 20 years experience
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Customer Question

Hello my audi A4 Cabriolet 3.0 litre manual 2002, is shuddering, or vibrating very badly. i have changed my catalytic converter and it is still doing it. i Have had all my coils checked, they are fine, I have had the engine pressure checked its fine, could you please give me a possible answer to this fault as it seems to be confusing every one. My car has been on numerous computers and no fault is being indicated. My only other option would be to take it to an Audi dealers to see if they can diagnose the fault. I have been told that it could be a bent valve or a cylinder fault. I changed both CATS and all the sensors

Submitted: 3 years ago.
Category: Audi
Expert:  AudiDoc replied 3 years ago.
Can you please tell me if an engine scan was done, and what fault codes were stored? This will allow me to give you some specific steps to attempt to repair.

Customer: replied 3 years ago.

Hi, no I haven't had an engine scan done, I have only had the checks I mentioned done. I don't know the fault codes stored, the car has been on various computers that give different readings but they all seem to be directed to the CAT hence why i changed it. A few years back Audi told me I needed a new CAT, I then took it to a specialist garage who advised me to try a Cleaner which is poured in the petrol tank, it worked for a couple of years. The car then started to vibrate and shudder after that from time to time so I continued to try using the cleaners, again it worked. Then it started to vibrate much harder, but it would start and stop when it wanted, it felt like a faulty sensor because of the pattern it took. Since November last year it has been constant, where as before the car seemed to cure itself. I hope this is some help. I went to one specialist whose computer was saying there are cylinder faults but that was only on there computer I got that information.

Expert:  AudiDoc replied 3 years ago.
If they're using an Audi specific scan tool, and are seeing cylinder misfires, I'd start to consider faulty ignition coil packs, especially if the engine light is flashing at times. The shuddering and vibration shouldn't be cat-related. I wish I could assist more, but without the faults codes, it's somewhat difficult.

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