I'm not a Lexus man but 1991 seems incredibly old to have A/F sensors. In any case you gotta pay attn on those A/F sensors. For example, on Camrys: 97-00 Calif spec 4 cyl, 98-00 Calif spec 6 cyl, 01 all Camrys except V6 w/ manual trans, and 2002 up all have A/... Login to read more.