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My problem is that the vehicle is idling High (Will go 10-15 Mph. without foot on accelerater.) and is running rich. I did some general cleaning and checked the vacuum lines. I unplugged the IAC sensor and nothing changed in how it runs. Checked the Check Engine Light, but nothing. To test, I unplugged the temperature sensor and that did trip the Check Engine Light.
My question is if there is a procedure to troubleshoot the wires leading to the IAC? I see that they go into another wiring harness and didn’t want to get to deep into it in case there is an easier way to fix it.
Any advice would be appreciated.
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Take you a screwdriver handle and tap on the IAC valve and see if the idle comes down. Fords of this vintage was common issue with the IAC valve itslef
I’ll try both of those suggestions. I guess I was centered on why the check engine light didn’t go off, but that means that the IAC could be bad, but it would not indicate it to me. At the same time, could the IAC be good, but if the computer system doesn’t detect it, it would not operate correctly? I traced the red wire and the white/blue wire to the main engine harness and they are good to that point.
The IAC valve controls the amount of bypass air coming into the engine to maintain a certain rpm range. The computer achieves this by rapidly turning the power or the ground on and off. This is called Pulse width modulation. this lifts the valve off the seat. the valve has a spring behind it to return it to the closed position. it is possible for the valve to stick either open or closed or somewhere in between. there is circuit monitoring for this valve which would set a code 12 which isn’t as specific as newer cars. Most likely it is controlled on the ground side. So with the engine running back probe both wires at the IAC with a multimeter test lead. One should have battery voltage and the other will have some kind of number that is switching or maybe around 5 v depending on the duty cycle. multimeters take readings and display the average so a 12 volt signal being pulsed to ground will be averaged on the multimeter. Hope that isn’t too confusing. You probably just have a bad IAC, very common.
I tested the lines. Red came in at 11.9 and the wht/blue wire showed a 134.0, whatever that means. I do have power to them, but it shrill won’t show a code. I’m guessing it might if I drive it around. I also unplugged it, when the engine was cold, and it did make a difference in how the engine ran, so the IAC might be Ok. I did notice that when I shut off the engine, there is the sound of air that continues for about 10 to 15 seconds. I can’t pin point it yet, but it is located between the IAC and engine wall, but is definitely not coming from the IAC. I have to get a person to help me and try to pin point where that sound is coming from.
Remove the IAC and tape over its mounting holes. If the idle speed then drops down though it did not when the IAC was electrically disconnected, replace IAC solenoid.
Check to verify that the throttle plate is closed and check for potential vacuum leaks causing the idle speed to be high
The electrical checks just confirm the IAC is being controlled by the PCM. The IAC can still be stuck open.I have not tried removing the IAC yet, got really cold here and has been snowing. I did unplug the IAC , again, and drove it for 10 miles, but did not trip a code. I then plugged it back in and removed the vacuum hose to the ERG and drove that for 5 miles, but it still did not trip a code. Removed the connection for the TPS and it tripped a code right away. Checked the vacuum hoses, but they look Ok. That is all for now.
I changed the IAC, while it seams more responsive, it still has the high idle. I also checked the mileage and only getting 9.8 mpg. In looking at other posts, I’m wondering if it is possible that the Oxygen sensor should be replaced. I’m guessing it has never been touched. I noticed it said they should be replaced on a more regular basis than I thought. If that Sesor is giving bad information to the computer, could that be causing some issues.
Update
Still have not solved the issue, but I purchased a diagnostic tool and am now starting to do research on the numbers.
KOEO both fast and slow, show no codes. KOER shows a Code 13 in both fast and slow that says, “Cannot Control RPM During Self Test, Low RPM Check. I take it that is because of the high idle. I can tell the computer is trying to slow it down, but can’t.
These are the numbers.
ECT(V). 0.6, ECT(F) 194, Engine Speed. 1328(Idles from the high 1200’s to low 1300’s), EVP(V) 0.3, EVR(%) 0, FUELPW1(ms). 6.4, IAC(%) 20, IAT(V) 0.7, IAT(F) 180, Loop Closed, Map(hg) 10.0, 02 Sen 1(V) 0.27, SPARK(~) 14, ST FTRM1(%) 8, TO Mode C/T, TPS(V) 1.0, V PWR (V) 14.1, V REF(V) 5.0Any suggestions would be appreciated. I did note that the Fuel Trim had been reading 1 to 2 percent, but was 8 percent when I recorded the data.
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