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Hi there, Common fault for many cars with P0171 and P0174 is purge solenoid stuck, carbon buildup in the heads, dirty injectors. I would perform an upper cylinder clean first. Remembering it has done 285000 miles. Gary
I appreciate the input, no one has mentioned any of those potential issues. Regardless, I'll follow up on the progress and thank you. R.D.
Hi again, Could be any of the above, not necessarily all of, start with the combustion chamber clean. Hope you can sort your problem. Gary