hi guys
im working on a 94 xj40 4.0 at the moment the car came to me originaly not starting ,on fitting a crank sensor she fired right up but im having problems geting her to run properly

i have vcm code fuel fail 23 oxygen sensor feedback (rich)

sometimes on starting the idle is unstable and sometimes the car will cut out if you dont keep the throttle open the other times she runs fine also the customer has told me that the car will missfire intermittantly

i have cleared the code but it comes back again after a drive

i have fitted an oxygen sensor and coolant temperature sensorbut it still seems to be running rich and intermittantly idleing badly also still logging fuel fail 23, i have also suspected the fuel preassure regulator but i have checked the fuel preassure and it appears to be normal

just wondering what other problems you tech guys have seen to cause this fault

thanks