I am looking for a bit of advice please.

I have a 2004 Carisma Equippe 1.6. A short time ago, the rev counter stopped working. About a week later when driving in heavy motorway traffic, the rev-counter suddenly went haywire and the engine management light came on. I had a diagnostic run on the car and it came back with a "misfire" code. After having the car serviced, the light went off. Last week, again when driving in heavy motorway traffic, the rev counter came back to life for a minute or two, before stopping again and the engine management light coming back on. Otherwise, the car appears to be running okay.

Has anyone had any similar problems or could they shed any light on potential cause?
Is it possible that the failure of the rev-counter could lead to the ECU mistakenly thinking that the car had misfired?
Is it worth getting repaired - any idea on what is involved and potential costs?

I have very limited knowledge regarding cars so any help/advise would be much appreciated!

Thanks

The Power Transistor sends the TACH signal to the PCM and instrument cluster. It also controls the firing of the ignition coils on this distributorless ignition system. A malfunction with it can cause it not to send a TACH signal and also cause a stumble/misfire.