agree with jap-s2k. get your injectors cleaned (new pintle caps, o-rings, etc as well) and flow tested and change your fuel filter. depending on how many km's your s2k has done and what sort of a service history it has may be what has caused it. also have a look at your spark plugs and see if they need replacing. if this doesnt do you any good, you might have to look into voltage readings from your O2 sensor and coolant temp sensor (yes the coolant temp sensor does play a role in a/f ratio's)
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