Possible IAC

Tiny
BUSTERSL2
  • MEMBER
  • FORD F-150
Hello everyone, yes another new guy with probably another common problem. My 1994 Ford F150 4x4, 302ci developed an abnormal idle over the weekend. The truck will start in the morning and operate normally. If restarted warm it will rev between 200 to 1800 rpm 3 / 4 times and then settle back to a normal curb idle. There is no check engine light and the truck does not stall, as of yet? Could this possibly be a idle air control valve problem? The EGR(OEM) has been replaced within the last 60days. I'm hoping someone can help me diagnose this problem.
Monday, March 27th, 2006 AT 7:21 PM

11 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Clean out your throttle body then comeback for more.
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Monday, March 27th, 2006 AT 8:02 PM
Tiny
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Will do, I should get around to it Friday. I'll keep you posted. Thanks!
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Wednesday, March 29th, 2006 AT 11:14 AM
Tiny
BUSTERSL2
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OK, I had a chance to clean the throttle body this evening. It was too dirty for my liking. After cleaning the TB the truck would not hold an idle and stalled. It also displayed a check engine light when the RPM would go over 1500. I started and held the throttle until all cleaner was burned out. And then disconnected the battery for 15 minutes. Afterwards the truck started fine and ran fine with no check engine lights, but I could feel the idle drop and labor every time I came to a stop? What do I do now?
This truck also has a ALT. Output of 14.7volts is this just alittle high? Thanks Buster.
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Wednesday, March 29th, 2006 AT 6:20 PM
Tiny
RASMATAZ
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You're ok with 14.7v. Now go back and open the EGR look around the pintle for carbon make sure it moves up and down. Also the manifold side-shine a lite in there. EGR don't cut it, we'll check idle speed stepper motor and Cold Start Valve or Injector, Perhaps maybe the Throttle Position Sensor for adjustment.

BTW about the Alty is this an Idle reading w/o a load comeback I'll be waiting just keep me informed is to what you have done and its results etc.
Too!
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Wednesday, March 29th, 2006 AT 7:19 PM
Tiny
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The alt. 14.7 is at curb idle to 3000 rpm with no change in volts. It also remained the same with every electrical option on? It seemed ok to me, but I may be wrong?
I'm not too familiar with the stepper. Is this the same as a throttle solinoid? And to check the EGR port all I do is disconnect it from the engine or the EGR from the tube leading to the engine?
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Thursday, March 30th, 2006 AT 9:28 AM
Tiny
RASMATAZ
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Alty is Okay
The idle speed control is somewhere within the throttle body-this is the one that maintains the engine speed at all times. Throttle Solenoid is something like the TPS Throttle Position Sensor. Have you check the TPS?
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Thursday, March 30th, 2006 AT 1:54 PM
Tiny
BUSTERSL2
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No sir, I have not taken much time other than cleaning theTB. I do have tomarrow off and will check and clean all throttle components I can. I will let you know the outcome after I complete these tasks. Thanks so much for your help. Buster
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Thursday, March 30th, 2006 AT 9:35 PM
Tiny
BUSTERSL2
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OK, I removed and checked for cleanliness of all the tb components. I reinstalled and checked for leaks and tightness. I was not sure how to adjust the TPS or how if I could on the step sensor? The truck seems to be running much better, however it still seems to be searching for the right idle speed with one rpm surge before it catches its self.
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Friday, March 31st, 2006 AT 7:12 PM
Tiny
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Ok, it's been some time and the engine will now stall just after it is started warm. You will need to hold the gas pedal down to keep it from stalling. Where should I start looking on this one? There are no check engine lights? I did just install a new TRS sensor for an irratic shifting problem? I'm sure the problem is in the TB, but how do you isolate these componants for troubleshooting?
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Monday, June 5th, 2006 AT 2:12 PM
Tiny
HEAVYDUTY
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It sounds like your Idle Air Control (IAC) is bad
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Monday, June 5th, 2006 AT 8:51 PM
Tiny
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Is there any way to check the IAC to make sure it is bad before you spend the money on a new one?
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Tuesday, June 6th, 2006 AT 1:51 PM

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