I bought a 2008 GMC Envoy with the 5.3 engine in it. About a year and a half later trouble codes started poping up. The check engine light turns on and off by it self and I dont know what to do. When the check engine light is on my gas mileage goes down from 16.2 to around 14.9. And the car doesnt take off as fast or downshift as fast.
I dont know what to do
Looking up the codes and their potential causes might be a good place to start.
https://www.carparts.com/blog/p3400-code-cylinder-deactivation-system-bank-1/
https://www.carparts.com/blog/p3425-code-cylinder-4-deactivation-intake-valve-control-circuit-open/
https://www.carparts.com/blog/p0106-code-manifold-absolute-pressure-baro-sensor-range-performance/
It's likely that P3400 and P3425 are triggered by the same issue. (P0106 might be a separate problem.)
I would de-activate the cylinder de-activation.
@bob81 how?
how?
A quick internet search for "AFM delete" comes up with answers within seconds, such as:
https://www.gm-trucks.com/forums/topic/235444-the-ultimate-guide-to-dod-afm-delete/