Although warmup related problems are usually related to vacuum leaks or the ECT, yes the secondaries can also cause this and it is worse when it gets cool out. The secondaries are strictly RPM operated.
Look under the throttle body for the secondary shaft ends and the linkage bars both between them and down to the vacuum operated dashpot. Have someone start the engine. they should close (they will even close just when the ignition is turned on if there is still vacuum in the reservoir). If they do not, test for vacuum going to the dashpot at idle. No vacuum means the IMRC vacuum solenoid bolted to a plate on the back of the rear head is bad.
Sometimes the system is working except the plastic retainers have broken and the linkage has fallen apart.
BTW if you were wondering, the secondaries are closed at low RPM to speed up intake runner air velocity and both improve fuel mixing and improve cylinder stuffing as the intake valves close.
