P0171 1998 chevy lumina ltz 3800

Question

I have a PO171 lean mixture, bank 1 code.
I have had MAF  sensor replaced twice. Check engine will come on  and sometimes shut off. Mostly on. Under hard acceleration, engine pulls strong (235,500 miles) but near redline there is a slight hesitation. Almost like engine not getting enough fuel. IDK for sure. I take excellent care of car and engine. Synthetic oil. Intake gasket replaced, as common problem with 3800's. I use 89octane, sometimes 93. Problem seems slightly better with 93. I'm guessing low fuel pressure or vacuum leak.

Answer 1

Vacuum leak is more common when you have a lean fuel trim, If the CK ENG LT comes on during hard acceleration, have a exhaust back pressure check, Using synthetic oil with this year make and model will do more harm to catalytic convertor.