Luz Check Engine Light Ford Ranger 2.3

Please can anyone help me? I have a Ford Ranger 2.3 year 2008 I was lit by the light Check Engine sometimes turned on and other times it simply went out but now it is fixed, they scanned it and threw error P2196, I started changing spark plugs fuel and air filters and the last was the oxygen sensor (which brings only one before the catalyst) .... What can be failing? Ah and changed the IAC valve.

The fuel pressure could be low or an injector begins to give problems, possible leakage to the admission or input of ristringid air and measure the signal of the acaccouous sensor to the manufacturer's specifications (short cables). greetings.