2007 Volvo XC70 Question: have a P2178 cel, originally had a P0101 and changed the MAF sensor and O2senso

The car has about 67,000 miles, a P0101 code came up and I changed the MAF sensor, all was good, idle was back to normal and not sluggish. then about 1 week later a P2178 came up. I checked for vacuum leaks and found none. Ran a bottle of Lucas injector cleaner through the tank and then put a new upstream O2 sensor in last weekend and the P2178 code has come back?????? What are next next steps to take?