The throttles are shut at idle and the required air is supplied via a separate circuit. When the engine is idling the throttles are bypassed via an idle air circuit. Provided the TPS is delivering the correct signal voltage, (0.5 volts) when the throttles are shut, and they are mechanically shut, there can be no adverse affects. This can be simply tested, as per my advice included within the how too stuff.
When the engine is cold, idle air is provided via the by-pass air control solenoid valve, together with the auxiliary air control valve. The latter is directly temperature operated and should shut as the engine warms up. The solenoid valve is controlled via a signal from the ECU, which depends on several sensors for the required information in order to set the idle speed for various conditions, when the engine is at normal running temperature.
A diagnostic check should show up any of several possible faults, with the exception of the auxiliary air control valve, which is a very likely culprit. If this does not shut when the engine becomes warm, idle speed will be excessive, as is the exact symptom reported. N.B. There is a constant 12 volt supply to this valve, even though it is not involved with the TCU.
An air leak post throttles, could also cause the problem. There have been reports of loose manifold bolts. However in view of temperature being a reported factor, this is a less likely cause.
I hope this screed may be of some assistance.
