UK Car Repair Questions? Ask a Mechanic for Answers ASAP
Hi my name is***** am a diagnostic technician and look forward to working with you.
The fault code you have is P0303 - CYLINDER 3 MISFIRE DETECTED which perfectly explains the symptoms you describe. I think at this point it is safe to rule out a vacuum leak. As you have changed the basics such as plugs and the coil packs I would advise you now swap cylinder 1 coil pack with cylinder 3 and clear the fault codes. When the fault re-occurs if the fault codes points to cylinder 1 misfire it is a coil pack problem. This is unlikely as they have been replaced but is worth checking.I suspect however this is a sticking valve rather than an ignition system problem. Unfortunately it is a very common problem on these engines due to the fuel system design. The TFSI Engine has the fuel injected directly into the combustion chamber rather than the intake port, this means the intake valve doesn't get cleaned by the passing fuel which in turn causes a build up of carbon and a sticky valve.Officially the correct repair method is to strip the top end of the engine down to physically remove the carbon build up as generally speaking once the build up is bad enough to cause the valve to stick, chemical cleaners are unlikely to help. As this is happening for a short time when very cold in your case I would strongly recommend you try a chemical clean such as Sea Foam or TerraClean. There is a good chance it will cure the problem, however ultimately unfortunately it is delaying the inevitable and in the future the cylinder head may need to be removed to give it all a good clean.Please feel free to ask if you have any further questions, if your happy with my answer please don't forget to provide a rating, thanks, Ross.