My 6.0l GMC won't idle when cold. No check engine light. Any Suggesttions?

. Replace platinum spark plugs (ACDelco only), with the exact plug that came in the vehicle, if the plugs have over 40,000 miles on them.

. Clean the Idle Air Control Valve (IACV), throttle plate, throttle body and ports:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post1054149

. Replace air filter.

. Check/replace Engine Coolant Temperature (ECT) Sensor, which affects fuel injector pulse width. The ECT Sensor is a temperature dependent resistor (thermistor), whose resistance decreases as the engine coolant temperature increases. It provides a richer mixture when cold, leaner mixture when hot.

. Check all vacuum hoses.

. Replace PCV Valve.

. Clean MAF Sensor:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1377134

. Adjust throttle cable, if necessary, to set idle rpm to specs.