Ford PWM IAC not working.

PJF · Post by **PJF** » Fri Aug 25, 2006 6:42 am

MS-II V3 2.36Code MT2.25

When I initially put my MS together I bought the Ford IAC kit from Jerry at DIYAutotune which consisted of a replacement Q4 and replacement R19. After my first start it was obvious the IAC wasn't functioning. My mulimeter showed Q4 had all legs with continuity to ground. So I had somehow burned it out I guess. The IAC valve was simply wide open any time the key was on.

I bought a TIP120 and did the other modifications in the Mega Manual and now the IAC stays completely closed when the engine is running. The only way I can get it to idle is with the throttle plate screw. Megatune is showing a change in PWM % while the engine warms up but there is no change in the IAC position.

One side of the IAC is wired to 12V and the other runs to the FIDLE spot on the relay board. I have a diode across the leads with the banded end going to the +12V lead.

I don't have access to a scope, only a VOM. But I do see +4.34 volts on the FIDLE lead. When I plug in the connection on the IAC itself the FIDLE lead immediately goes to +12v. Do I have a bad IAC? Is my TIP120 installed wrong? I assumed I would see ground on the other leg of the IAC.

Any help is appreciated!

Bernard Fife · Post by **Bernard Fife** » Sat Aug 26, 2006 6:03 pm

PJF,

Is the tab of the TIP 120 insulated (with a mica insulator)? If not, it grounds the source, and the PWM doesn't work.

Lance.

PJF · Post by **PJF** » Sun Aug 27, 2006 4:06 am

Hi Lance-

Thanks for the reply.

The TIP120 is actually just soldered into the proto area of the V3 board. So no chance of grounding out the tab.

Should I just bite the bullet and pick up a scope on E-Bay and see what I am getting on the FIDLE?

Thanks.