The first thing I would do is get underneath and see if any wires were damaged by the (off)road debris - I have seen this happen several times (on other vehicles) where the wires to the oxygen sensor get damaged and cause drivability/fuel consumption problems. Also, did you mean something besides 1/2 on the gauge? 1/2 seems normal to me. Anyway, best of luck. Also, I'm new here and new to Monteros for the most part, so there may be an obvious fix that I don't know about.

Nick

'91 LWB, 31x10.5s, KYBs, A/T "I look like Robert De Niro, I drive a Mitsubishi Pajero" - Billy Bragg (not the original lyrics, but that's how he sang it when I saw him in Dublin in '04)