I have an A5 Cabriolet Diesel Turbo 3.0 and the coil light came on 1 day ago and the acceleration in the car has vanished but the car will pick up momentum and still able to reach speed required albeit it now takes a 1/4 mile. What do I need to do.. Please..

 

It means there is something wrong with your glow plugs. They are like spark plugs but their main function is to heat up the combustion chamber to allow diesel to ignite. With the weather turning cold now, the engine is too cold so you need longer time for the engine to warm up. Does your car drive better after it's warmed up?

I have a 1.9 TDI that needed the glow plugs replaced. It's not hard. Almost like a spark plug if I remember correctly.

It could also be the glow plug wiring harness that's frayed or cracked or lose and thus is not sending all the power to the glow plugs.

The harness is only a tiny bit harder to replace (at least on my 1.9 TDI) since they were not designed to be replaceable, so I had to cut out the old one and solder/connect the new harness.

Good luck!

Alex