Ok I have been having trouble out of my truck the past few weeks. Its a 01 with a 5.4 in it with 150,000 miles on it. It has been a great trouble free truck up to now. Now to the problem.

When you start the truck it does not idle up to help it warm up. It goes to 500 to 600 rpm only. An when it is cool out I have to give it gas to help it warm up so it will run. I try to hold it to about 1100 to 1200 rpm to warm it up. While it is idleing when cold the idle surges up and down. I have replce the MAF on it. The old one when bad and the truck would hardly run at all, it was missing like crazy. After doing that it would not idle. So I tried cleaning the IAC. That did not help so I replaced that. Still no help with the idle. I have also replced the PVC on it.
When I was having trouble with the truck missing real bad. I tried to clean the MAF, IAC. That didnt help so I replaced them with new parts. And sprayed some throttle body cleaner in the throttle body. Could the cleaner have gotton on the TPS and messed it up?

Thanks sorry for such a long write up. If anyone has any ideas please let me know. Thanks again

 

Your IAC is bad or your computer puked. Then it could be a broken wire. You should have a CEL with this issue. I would replace the IAC myself.

 

The IAC is closed and non operational for some reason.
500 rpm is about the normal min. 'throttle stop' idle speed when the IAC is unplugged or stuck closed..

 

The IAC is new. I put it on Friday. I guess I could have gotten a bad one. I will check tomorrow if there is any power to the plug with the volt meter.
Bluegrass 7 do you know if I take it off and turn the kye to the run position will the ICA open? Or does it work from vacume when the truck starts?

Thanks.
Bear 45/70 I will also check for a broke wire, An I hope the computer didnt puked.

 

The IAC is 'pulsed' by the computer.
It's all electric, no other control.
Here is what is supposed to happen with cold starts.
When you turn the key to run, the PCM looks at the value of the head temperature sensor and the intake air temperature sensor as the only way the PCM knows what the starting conditions are to be.
The PCM then sets ignition timing usually advanced, allows more fuel by injection (from a fixed table) and opens the IAC to allow more air that raises the idle speed.
In about 45 seconds the OX sensors heat enough to begin outputting there signals to begin controlling the fuel injection amounts (the fixed tables are now disreguarded).
As the heat builds, the idle speed begins to drop to full warm status so the idle drops back to about 750 +/- a small amount.
Note; the colder the start temperature the longer the high idle stays up.
All the functions are completely computer controlled.
It simulates a carbed motor but with much more control, no stalling and cold drive-away unless there is a fault.
Good luck..

 

None of my EFI Fords have every idled at 750. 1000 to 1100 is what all 4 of mine see.

 

....Hot Idle is a set value in the program tables.
....The crank sensor is the RPM indicator that tell the PCM what the RPM is at any given moment.
....The PCM makes corrections to the idle speed by varying the IAC opening on a continious basis to keep the hot idle within +/- 50 rpm in a fault free system.
....An idle at any other speed is a fault in a fully heated motor.
....Some try to set the idle by changing the throttle plate stop to attain an idle rpm but this is never a correct thing to do because the ability to fully control the idle by the PCM is lost when load changes occurr such as A/C, lighting and other loads change the idle rpm such that it cannot be corrected with the IAC control.
....Also, trying to lower the idle with this stop causes the same type issues plus the throttle plate can become stuck in the throttle housing bore after cool-down. Hence the 500 rpm setting without IAC and the 750 with it connected.
....Excessive idle at anything above 900 causes creep at intersections, causes more transmission heat. Not desireable.
Good luck.

 

Thanks Bluegrass 7. I took the new ICA off and took it back and got another one. Hopping the new one I put on was bad. No luck nothing changed. I looked for broke wire and found nothing. Guess I will give up and take it to ford. I was realy hopeing to fix it my self and save some $$ this time of year. The engin light is not on so no codes. Thanks for everyones help.


Tim

 

I'm sorry it did not work out.
All you needed to do was pull the connector off while the motor was at idle.
If the idle changed at all the IAC was working to some degree.
If no change then the IAC has no control of the idle.
At the dealer, the tech can look at the IAC signal and see if it is being controlled with their test equipment or if some other fault is present.
Good luck.

 

Ran into same problem ended up being the IAC

 

No CEL does not mean there are no codes. So codes do not set the light.

 

Its still not fiexed. It has got warm out side and it runs better. Still dont idle right. I have replaced the iac and an thinking about replacing the maf again. Its still under warrnty.

 

The IAC is the only part that controls idle directly, the same as you throttling it up with the gas pedal to admit more air.
It is powered like many other parts from the PCM power relay.
One lead goes to the PCM to be pulsed as the way the idle is continiously controlled while the motor is runnig.
The crank sensor tells the PCM what the RPM is at all times so the program can open or close the IAC to make the idle correction be within the idle table value.
Have you measured voltage to be sure it's getting power?
If no parts are the cause then the lead to the PCM is open or the PCM cannot output a signal varied ground to control the IAC..
As stated, the tech can look at all this and see right away what is not working as it should.
Good luck and let us know how it went.

 

Thanks bluegrass 7. I will try to find someone that can check it. I will let you know. Thanks again


Tim

 

Bluegrass 7 I did check the voltage. It is getting power to the IAC. I did find a big vacum leak last night. I had not noticed before. It is where the cold air intake tube conects to the throttle body. The rubber part that conects the intake tube to the throttle body has the two hoses that goes to the drivers side. The one on top goes just in front of the IAC.the bottom one goes to the drivers side valve cover. The top one is leaking bad real bad. I am going to replace that rubber part an see if that helps.

Thanks again for all your help