I’m in the military overseas and having a starting problem with my 2006 Ford Five Hundred. When the weather is cold, around 45 degrees F or lower the car starts OK however within about a second the RPM’s drop between 400 and 500 and the engine starts to stumble. After about 3 to 4 seconds the RPM’s gradually increase to around 1300-1400 RPM and is OK at that point. Any ideas since the overseas mechanics are not that sharp.
The Idle Air Control valve might be hunting during a cold start. The IAC valve is what controls the engine idle speed under all conditions.
The next time you go to start it cold and it displays the same condition, slightly tip into the throttle. If doing this allows the engine to idle smoothly, most likely the problem is with an IAC valve being effected by the cold.
I replaced the coolant temperature sensor on my buddies saturn to fix the same issue. As the widget started to go bad. When these go bad the car thinks it’s either crazy hot or crazy cold and the computer tries to compensate with the fuel/air ratio. I recall the part was about $10. General instructions are to pull the electrical connection, pull out the old one, put in the new one, replace the electrical connection. The one tip that I can offer is that you should wrap the threads with teflon tape prior to pulling the old one to make the swap quicker. The saturn lost about a quart of coolant since the sensor was below the coolant level (makes sense if you think about it).
Thank You very much for the information. Next time I start the car I try what you have stated. Once again. Thank You from South Korea, U.S. Army.
Just fixed an '05 500 friday with this exact symptom. Had to update computer.
I will be taking the car in for service at one of the local shops that work on Fords. Will try your fix first as the IAC Valve is part of the throtle body and cannot be replaced individualy as it is all one assembly. This according to a Ford Dealer back in the States. Thank You for the info.