As the title says. I've replaced my Mass Airflow Sensor and my idle air control valve. Yet when I have the idle air control valve plugged in, it idles fine on startup, but after going into first it will always increase RPMs when I push in the clutch. Happens throughout the entire drive through all gears.

Any ideas?

(2002 3.8L BY)

 

Your cars computer is making idle calculations from various sensors. One of those during driving is the vehicle speed sensor. So what it is doing is every time you press the clutch while the car is moving, the computer raises the idle between shifts to avoid any hiccups in the MAF system. When you release the throttle between shifts it creates a pressure wave inside of the manifold. This pressure wave is enough to cause the car to stall when coming to a stop, or cause undue stress on the drive line between gears. To mitigate this, ford and other vehicle manufacturers, have programmed the computer to bump the rpm up between shifts, this counteracts that pressure wave from going back up the intake tube and causing fuel/timing problems. The MAF is a very sensitive sensor and any sudden changes in air flow or pressure across it will cause the car to miss or stall.

In earlier days, when MAF was introduced, guys started to convert the speed density cars over to MAF. One of the first things that you will see with this conversion is that if you do not add a speed sensor to the harness, the car will either stall or almost stall at stop signs when you let off the gas. This is why when doing a MAF conversion you must make sure you add that speed sensor harness. If no speed sensor is added, the idle must be set higher to compensate for this.
The newer MAF cars do this automatically between shifts and when coming to a stop. You will notice, that if you are coming up on a stop sign and hold the clutch in,, the idle will jump up and stay there until the car comes to a stop.