yo, You habe an 89 Bronco II, right?
Idle Air Control (IAC) Sludge; Poor Idle TSB 91-25-07 for 85-92 Bronco & F Series & many others; "...Hard cold starts, hesitation and stalls on initial start-up or during idle or decel may be caused by sludge in the throttle body and/or idle by-pass valve. Sludge deposits or oil film on the throttle body bore and plate or the idle air by-pass valve may cause one or more of the following conditions. Hard Cold Start, Stall On Initial Start-Up, Stall During Idle, Stall During Decel, Rough Idle, Rolling Idle, Hesitation During Acceleration. A new idle air by-pass service kit (F2PZ-9F939-A) is now available for service use to correct sludge contamination concerns of the throttle bore and plate only. It eliminates the need to clean the majority of past model throttle body applications. Cleaning is not required on sludge tolerant throttle body designs released for 1991 and newer model years..." Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net
Click on the baove and read through it; it is long, detailed and exact as per Ford's instructions...
some think it's too long to read & miss the important info.
========
The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows air, determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.
Removal & Installation
1.To remove the IAC valve, first disconnect the negative battery cable, then the IAC wire harness plug
Next, remove the two IAC valve attaching bolts ...
... and pull the valve from the intake manifold
2.Disengage the wiring harness connector from the IAC valve.
3.Remove the two retaining screws, then remove the IAC valve and discard the old gasket.
When installing the valve, always discard the old gasket and install it using a new one
by Ford & CHILTON
4.Clean the IAC valve mounting surface on the throttle body of old gasket material.
5.Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71-106 inch lbs. (8-12 Nm).
6.Attach the wiring harness connector to the IAC valve.
7.Connect the negative battery cable
GL!