Fuel mileage is terrible (13 mpg,18 lp100km)with engine check light comming on. on 2007 Toyota Tacoma

Allready retrived P0138 code, replaced with Toyota rear O2 sensor, day later CEL back on, flushed out badly gummed up EGR value and connection lines. Day later CEL comes back on. Exhaust sounds rough. Has only 52,000 km. Giving ~ 13 mpg = 18.1 liters per km
Been to garage 3 times, diagnosing symtoms not cause ?

Asked by for the 2007 Toyota Tacoma
fuel trim issue seek diag and save time and money