954runner running too lean?
 

Hey guys! I'm new here, but I have searched around to try to find the answer to my problem. So I bought this 95 4runner from someone off CraigsList, he screwed me. I've had the engine torn apart and have put more than I paid for it into parts and labor. Anyways, when I got it the valves were too tight, causing too much compression, brakes went out etc. Had that fixed but now it won't pass smog because it's running too "lean". I hooked it up to my OBDI code reader, only 1 code came up and thats: "running too lean" but doesn't say where. I searched here and found a thread mentioning the o2 sensors, I unplugged BOTH (1 at a time then both together) with the car on, gave it some gas and didn't notice a difference in the sound (there's been a gassy smell since I bought it, but Toyota said maybe because of the type of exhaust the previous owner installed.) Anyways, how would I know if I need to replace the o2 sensors and if I do, would that really prevent it from running lean or could a vaccum leak cause it to run lean also? My fuel injectors are still good but the little green plastic cap on top of them is cracked, a mechanic put something over the cap temporarily until I become rich and buy all new injectors lol. Also, my exhaust has little white holes in it like it burnt through and the whole exhaust is welded together, is that normal?
Sorry for all the questions, I'm a first time toyota SUV owner, even though Toyota's run in the family. Thanks in Advance for any help!