Hi everyone, I am new to this forum. Just hoping to get some advises from you professional guys since I am a car idiot. Sorry for my long story……but I really want to get my beloved car sorted.

I drive a 1998 jaguar xj8 4.0. About two weeks ago, the car start to came up with some problems, such as the engine noise being gone noisier and not smooth after that the car start to vibrate and being rough once started, and it shakes more rigorously when the engine was heated. However, none of the warning lights came up at all.

Today, I get all my coils replaced, a new air filter fitted. After that, I started my car again. Result is the car doesn’t shake anymore, engine sounds as good as before. But sadly, the "restricted performance" appear on my dash this time.

Therefore, I turned off my car, and decided to re-check everything and see whether I have miss out anything. I found out I forgot to reconnect the plug, which connected to the air intake pipe.

After I reconnected the plug and start my car again, the “restricted performance” thing had gone, but the bad engine noise and shaking is coming back again.

I have absolutely no idea what is happening to my car and how to solve it. I deeply hope that someone could give me any suggestion on what problem it may be…

Thanks very much for your help!!