I have a 99 F-150 with a 4.6L and about 68k miles, when the weather is cold 15 degrees or colder the truck will start run for about 2 seconds then quit in order to get it to run and keep it running I have to hold my foot on the gas pedal until it can go on its own. Any and all help would be appreciated.

 

It's likely that the IAC valve is sticking in the closed position. The Idle Air Control valve is the sole inlet for air into the engine whenever the gas pedal isn't pressed. Pressing the gas pedal opens the throttle plate and offers an alternate source for air. An IAC valve is about $70+ at the dealer, and is a DIY job, particularly on the 4.6 engine, which has the valve located in a more accessable area than the 5.4 motor does.

How to locate and replace the IAC (4.6 liter engine specific location)

1. Remove negative battery cable from battery. Turn on headlight switch to ensure all current is drained from system. Turn climate control switch (not blower fan switch) to "OFF" position. Why? See below.

2. Remove three bolts that hold black plastic 4.6 cover from top of engine. (10mm I believe) You might find a small black pad (loose) sandwiched between the cover and one of the induction components. Remember where it goes.

3. The IAC should now be visible. It consists of a silver cylinder crimped onto an L-shaped fitting that is attached to the intake manifold by two 8 mm bolts and has a two-wire harness (red and white wire or red and yellow wire). It's on the driver's side.

4. Unclip harness and remove 8 mm bolts, remove IAC. Carefully remove black gasket on bottom of IAC and save for reuse; OR buy a new gasket (Ford treats this as a separate part - not included with IAC purchase).

5. Install new IAC on manifold. Don't forget the gasket. Reattach the wiring harness.

6. Turn off headlight switch. Reattach negative cable to battery and start engine (leave engine cover and attaching bolts off and OUT of engine compartment for now).

7. Start engine, leaving climate control system in OFF position.

The engine computer software and the new IAC have to become reacquainted with each other. The computer has to relearn how much current is required to move the IAC shaft over it's operating range. Let engine idle for fifteen minutes with the climate control off. Assuming everything is OK, reattach plastic cover after turning engine off.

Done. Ford will charge about $100 in labor for this procedure.