Code 12 & 13 help please!

FoMoCo17 · Oct 20, 2011

1990 Mustang GT

I have been getting codes 12 and Code 13 lately. Over the last year and a half I have put 4 Idle Air Control valves on my car cuz they just do not seem to act right.

Recently, I started getting the above codes after a new IAC that had been on the car about a month. MAF was also replaced with a new unit. Anyway, I checked the resistance and it seems fine ... think it was like 9 Ohms. Checked the power feed and got battery voltage with key on ... and got 14 volts with engine running. Checked the other wire that the computer grounds (forgot the pin) and it ranged from 7 - 8 volts with the engine running and varying the throttle. My book states that it should be between 3 and 11 volts varying throttle not sure if this is good enough even though it is within the range. Any other ways of checking these IAC's out properly? its hard to believe something is wrong with these things since its been more than one that I have put on here. Additionally, the car starts up and immediately stalls. Usually have to start it 2-3 times and it also runs rough. When I do the KOER test, it doesn't seem to kick it up and down as it usually has. Adjusted idle several times but nothing seems to make a difference. Passageways are all clean since it is new.

Can these IAC's be tested across the battery like other solenoids can be briefly? Seems like they should be w/o causing any damage. Could tightening down these IAC's be causing the housing to bind the valve or something? Any body have any ideas or experienced this before?

jrichker · Oct 20, 2011

Don't wire an IAC directly to the battery - you may damage it.

IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An Oscilloscope is even better if you can find someone who has one and will help.

Recommended procedure for cleaning the IAC/IAB:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damages some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. Reassemble and reinstall to check it out.

Gunk Dip type carb & parts soaker:

Code 12 & 13 help please!

FoMoCo17

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Code 12 & 13 help please!

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