Land Rover Repair: 99 Discovery Series I, rocker shaft, rocker shafts

Question
John,
On January 5th, I had a rocker shaft break in my Gems engine with 185,600 miles. This only affected the #1 exhaust valve and I parked the vehicle once this was determined. I spent the days waiting for new parts cleaning all of the rockers, and push rods, then replaced both rocker shafts, changed the oil twice, changed plugs and cleaned and inspected the coils and wires. The evening I put everything back together, the truck ran well, but after three days of driving, I am getting code 1158. I am clearing it once or twice a day, and it keeps coming back. Before this event, I never had any codes or MIL light, and passed emissions with no problems. Ideas on what I should be looking at?

Answer
The question is . . . Is this coincidence, or did you cause the problem?  I'd look very carefully at your work with that in mind.  The code is for an o2 sensor rich signal, which could mean the sensor is failing, or the cylinder is rich due to injector trouble, or the engine has a skip, or there is an internal problem related to the rocker that broke.