Right when the Tigra is floored it punts out a small amount of black smoke (over fueling) and just recently its been stuttering whilst just driving at a constant speed (about 50 mph).

The engine is totaly standard.

What could be causing this? Do they have a Lambda sensor and could this be causing this? and if so how do i get it checked?

And is there anywhere in the Kent/south east area that has a rolling road and is a Vauxhall specialist on these engines?

All help or advice is greatfuly recieved as i aint got a clue about it.