Misfire above 4k
Hello,
Hoping someone can help, I have an 05 Festat ST with 53k on the clock and it has developed a misfire when over 4k the car judders and you can hear it missing. When idle there is a slight burble but not that noticeable. Also when you blip the accelerator idleing it hold the rev’s for a split second before settling back down. So far it has not done it under 4k.
I have cleaned the induction kit and the throttle body, I have had the plugs out and they seem fine a little black but nothing uninspected.
Any ideas what it could be? I was thinking coil pack but that would miss all the time?
Thanks,