Our first and most important recommendation is to pay for and obtain an accurate smog check failure diagnosis; which should pin point your Chevy Suburban's rich mixture problem. Following a smog station's "suggestion" on what to repair could end up costing you hundreds in unnecessary repairs.
The repairs you've conducted so far should help lower emissions however if a rich fuel condition exists due to an ECU error, meaning a fault which is commanding the fuel injection system to delivery more fuel than necessary, only an accurate diagnosis of all your vehicle's emission sensors will suffice; specifically the oxygen sensors.
We recommend after a basic visual look over and verifying mechanical functionality (ie. spark plugs, air filter, fuel pressure, cylinder compression) a smog station conducts a "fuel feedback test". This test includes ensuring the oxygen sensors are working properly, your vehicle's emissions computer is receiving the signals from the oxygen sensor, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. Along with checking the oxygen sensors, the MAP (manifold absolute pressure) sensor, TPS (throttle position sensor) sensor, and ECT (engine coolant temperature sensor) sensor will be inspected as well. More on high CO below...
What causes high CO?
