judders between 5 & 6k revs

Rev it hard and then turn off your motor.

Pull the spark plugs. Number them to match your cylinder numbers.

Take a good close-up picture of each plug and post it here.

Also, see the blue link below on reading spark plugs.

 

1) Was it misfiring BEFORE you had the service done, or did the problem start after the service?

2) What kind of a service was done? Full, engine-out service with a new timing belt, or a minor service? Were the spark plugs replaced at that time?

Sometimes, when you have a mysterious engine problem like this, it turns out to be a bad connection at the two crank sensors at the front of the engine. Might be worth the effort to check these.

Good luck, And welcome to Ferrari Chat!

 

There's a whole bunch of things that COULD cause the "judder" you are describing. If the plugs are new/recent, you should be able to rule them out unless one was damaged by dropping it, or the threaded caps on the ends of the plugs are loose. It still could be the plug wires. It could be the ignition modules. It could even be a faulty alternator, or a bad engine ground.

But I think the first place I would look would be at those crank sensors. You have to get underneath the car and pull the splash panel to get at the front of the engine. Look at the picture where I have placed the arrows. These are the sensors. Unplug the wiring connectors to them and look at the pins, and look at the wires where they attach to the pins. Make sure everything is clean and tight, and that the wires aren't broken. There have been many cases reported here where those sensors were at fault.
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See post #2.

 

I'm sure all of us are very pleased to hear that your problem turned out to be something simple. Could you let us know what bolt was responsible? It sounds rather incredible.

 

Had exactly the same problem - but misfire at 4000 rpm

Data cables were loose and dirty - problem solved
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Hello, just to give you some info on my findings with "juddering". The car ran great until the oil temp was about 100 C
then it started to hesitate at 6000 rpm. My fix was to replace all the HT leads, seems that the old leads lost there insulation when getting warm
and the spark went to ground instead to the sparkplugs.

Marcus