Engine control computer

Tiny
QFONG
  • MEMBER
  • 1995 FORD CONTOUR
  • 2.5L
  • V6
  • FWD
  • AUTOMATIC
  • 129,000 MILES
Why is idle air control valve getting a constant 12 volts causing the engine to idle at 3000+ rpm? I had to disconnect it.
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Monday, March 14th, 2016 AT 8:10 PM

12 Replies

Tiny
CARADIODOC
  • EXPERT
12 volts is applied to the idle air control solenoid on the same circuit that supplies the injectors and other parts. Idle speed is controlled by the Engine Computer bringing the other side closer to ground.

Ford had a pile of trouble with the coolant temperature sensors in the early '90s. There's only one part inside it so they're normally extremely reliable, except for these. The resistance can bounce around confusing the computer into thinking it needs to raise engine speed in response to cold air coming in. That's a good suspect to start with.
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Monday, March 14th, 2016 AT 8:47 PM
Tiny
QFONG
  • MEMBER
I'll try replacing the temp sensor but it's going to take me awhile. Thanks for the tip.
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Tuesday, March 15th, 2016 AT 3:03 AM
Tiny
CARADIODOC
  • EXPERT
I learned this after a former student had this problem with his Taurus. I never taught my kids to measure sensors except to verify that they found the cause of the problem and to learn how the circuits work, but in this case a resistance reading showed the value to be bouncing all over the place. That is extremely unexpected since temperature sensors have only one part inside. That is a temperature-dependent resistor, known as a "thermister". I have to guess there was a mechanical break in the resistor or one of the wires attached to it. After I mentioned that to a friend who worked at a Ford dealership, he just shrugged his shoulders and said they ran into that very often. For that reason, suspect that sensor first before looking for other causes of your idle speed problem.

If you have a temperature gauge on the dash, you should have two coolant temperature sensors. The gauge uses a sensor with a single wire. You want to look for the Engine Computer's sensor which uses two wires.

If the CTS doesn't solve the problem, you'll need a scanner to view live data to see what the computer is seeing when it reacts by raising idle speed. You'll also be able to see if the computer is actually requesting that higher idle. If it is not, suspect a vacuum leak. That will cause a high idle speed without a corresponding increase in power.
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Tuesday, March 15th, 2016 AT 4:09 PM
Tiny
QFONG
  • MEMBER
Again, thanks for the info. I need to keep this car running.
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Wednesday, March 16th, 2016 AT 6:24 AM
Tiny
M_H_RITZEL
  • EXPERT
Come from a old school, first thing we would check is the wiring, make sure there is not a frayed or wire that is grounding out. That would send a false signal to the sensor.
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Wednesday, March 16th, 2016 AT 8:22 AM
Tiny
QFONG
  • MEMBER
Maybe I should run a new wire. Thanks for the tip.
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Wednesday, March 16th, 2016 AT 10:03 AM
Tiny
KEN
  • ADMIN
Please let us know how it goes so we can help others
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Wednesday, March 16th, 2016 AT 2:34 PM
Tiny
QFONG
  • MEMBER
I did all the above changes plus installed a refurbished ECM by Cardone. The car is now running and drivable but the IACV is still not working correctly so I put some resistance in line and got the idle speed down to 1100 with AC off and car in neutral.
Now with the different computer, the shift points are higher than they should be, similar in the older cars to the TV rod being out of adjustment.
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Tuesday, March 29th, 2016 AT 7:41 PM
Tiny
KEN
  • ADMIN
Sometimes it takes time for the new computer to learn the transmission, here is a wiring diagram, you can see the wires come right off of the computer, have you done a pin to pin check?
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Monday, April 4th, 2016 AT 1:34 PM
Tiny
KEN
  • ADMIN
Sorry here you go, please let me know.
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Monday, April 4th, 2016 AT 1:35 PM
Tiny
M_H_RITZEL
  • EXPERT
I came from an old school, so do not know if this will work, pre 80s cars you could reprogram the computer by just unplugging the positive terminal for a second then hook it back up. A lot of people would do this prior to bringing the car in for emissions check, then somewhere in the 80s they stopped it. Then one would have to drive the car about 40 miles until the computer would read everything and reset. With another ecm you put in, it might work in reading the engine and transmission. As I said I come from a school that had flat head engines and no emissions, so I don't know if it would work on your car. Ken has more experience in that than I do.
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Monday, April 4th, 2016 AT 4:24 PM
Tiny
KEN
  • ADMIN
Please get back to us so it may help others
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Tuesday, April 5th, 2016 AT 2:19 PM

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