After reading many posts on this hard to track problem and chasing the codes for a few weeks I was able to fix the problem. I read so much about the MAF and O2's being possible causes that I changed those right off the bat. They were due anyway. Well that didn't fix the problem, so I did multiple brake cleaner vacuum test on my lines to no avail. I finally caved and took it to a shop for diagnoses and the mechanic told me it was the lower intake manifold gasket, I was surprised because it had been changed with the heads 30K/mi ago. At the last minute I decides to do the job myself instead a pay a small fortune and I'm glad I did because when I got down there the gasket appeared fine. So I put in the new one anyway and did the water pump, thermostat, coolant resevoir and coolant lines while I was in there, cleared the code and drove for about 60 miles and the light came back with the same codes. So no fully frustrated and ready to trade it in for an LR3 I did one last test with the brake cleaner and sprayed everything tracking the problem to the fuel injectors. The O-Rings were shot, the fuel rail came out without any resistance. Ordered and put on new ones (just the bottom 8) and problem solved. Code has been cleared for weeks now and I finally passed inspection. Don't overlook those injectors!

 

Were you at any point getting o2 codes as well? like p0150 or p0130?

 

The only other code I got along the way was P0443 which is Purge Valve Open/short Circuit. I think that was just coincidental. I didn't mind doing the O2's as they were probably close to there end anyway. If you are getting O2 codes as well then you have more pieces of the puzzle then I did. P 1171/74 are so vague, it leads to a lot of digging around.