Just checking Google came across this seems it was an Earth on the throttle body for this lad , but as you say it could be any amount of things never heard of it before now 😬 Could have a leak somewhere before the o2 sensor causing It to not read the a/f correctly? Or a leak in one of your vacuum pipes maybe Hopefully someone can point you in the right direction 😀 http://www.toyotanation.com/forum/59-tercel-paseo-starlet-sera-forum/72614-92-paseo-check-engine-code-25-running-too-lean.html#/forumsite/20543/topics/72614?page=1