Every time I turn my A/C on my truck the RPM goes up and down

Tiny
ABEL TALAMANTES
  • MEMBER
  • 2005 FORD F-150
  • 100,000 MILES
The rpm goes up and down like it wants to stall, is it the throttle position sensor?
Wednesday, August 8th, 2012 AT 12:35 AM

52 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Most likely not. Look for any vacuum leaks first. If all ok, I would look at the iac motor. It may be bad.

Roy
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Wednesday, August 8th, 2012 AT 12:58 AM
Tiny
ABEL TALAMANTES
  • MEMBER
  • 4 POSTS
Where exactly could I look for leaks sorry im not good with engines. Is it in the intake?
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Wednesday, August 8th, 2012 AT 1:00 AM
Tiny
ASEMASTER6371
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Yes, along the intake manifold. You may need some help if you are not familiar with this operation

Roy
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Wednesday, August 8th, 2012 AT 1:11 AM
Tiny
ABEL TALAMANTES
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  • 4 POSTS
What would replacing the throttle position do?
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Wednesday, August 8th, 2012 AT 1:14 AM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
First check to see if the A/C is cycling as fast as the speed variation, if it is only doing it in conjunction with the A/C on I doubt that it will be a faulty IAC.
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Wednesday, August 8th, 2012 AT 1:37 AM
Tiny
SALVADORMENDOZA
  • MEMBER
  • 1 POST
This also hapen when u or I turn off my engine of 2002 f150 and turn on like hour later rpm needle goes up and down like for a 4 minutes look s like normal because I take the truck to cervise they never find enithing in my opinion this us nothing to worry about hope this help
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Wednesday, August 8th, 2012 AT 6:52 PM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
Sounds like the throttle body sensor, Under normal conditions when the engine is running each time the air conditioning kicks on there will be a drop in idle speed. This is caused by the extra strain on the engine. When the compressor shuts off then it should be normal. As far as the reving up, have found that the position sensor can make the truck do that.
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Friday, August 17th, 2012 AT 2:31 PM
Tiny
ABEL TALAMANTES
  • MEMBER
  • 4 POSTS
So it isn't the throttle position sensor than? Or could it be the vacuum that's dirty because when I trurn the ac on and the Rpm goes up and Down. Then I step on it on park or neutral the truck dies.
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Saturday, August 18th, 2012 AT 6:08 PM
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
  • 2005 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 100,870 MILES
I just replaced my battery, I did what the owners manuel said do by letting it idle after replacing it. Had no issues before the battery was replaced, now it either dies when I come to a stop or almost dies. Any suggestions would be greatly appreciated. Thanks
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
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In what order did you re attach the battery cables? Did you check the ground wire pigtail if it has one? If it was damaged, or broke off the fender, re attach it too! Try disconnecting the battery for at least 5 minutes, remove the negative cable first, and put it back on last! This will clear the KAM, Keep alive memory, and you can now do a new relearn.
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
Thanks for the reply, I'll do what you suggested. I think I did just the opposite of what you said. Thanks again
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
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OK keep me posted.
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
Thanks merlin2021, that did make a differense. Still has some hesitation at stops sometimes but much better. Seems to be getting better the more I drive, hope it will work itself out. Thanks again
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
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OK, you might also want to check the rubber PCV elbow, they tend to dry rot and allow vacuum to escape, try replacing that too. Ford has a good supply of these on hand. It's a well known problem!
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
Still got some drama. My truck still didn't seem to be getting back to normal so I stopped by the Ford dealership today to get some advice. They checked it out and said I need a new throttle body. Just needing some thoughts on this. The truck had no idle problems what so ever before changing the battery. Could this just be that the throttle body just went out at the same time or is there something as I can check. Thanks for any help you can give. Terry
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
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Is the check engine light on? Autozone can read the codes if any and they do it free, Post all codes found.
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
No check engine light on. I will go to Autozone to see if any codes come up. Thanks
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
Went to Autozone had the codes checked. It came up with code P0506. The check engine light did come on yesterday. It surges up an down at idle. Code says
1) Vacuum leak on engine ( I looked every where I could didn't see anything.
2) Dirty throttle body
3) IAC motor defective
4) Poor electrical connection to the IAC valve.
Thanks
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
The IAC is a common problem on these anyway, get a can of spray Throttle body cleaner, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! If that doesnt do it, you may need a new idle air control valve, it's bolted to the throttlebody
Clean out the throttle body too. Do it with the motor off, and use a rag to wipe the carbon off with the tbi cleaner. If this has the electronic throttlbody, there is no IAC. Clean the throttle body, it may work, taking it off to clean will yield better results! Ford states these throttle bodies are not to be cleaned. Think Toyota here. Electronic throttle control is tricky stuff, NASA is involved with figuring out Toyota's problem, so you really do need to be a rocket scientist nowadays! BTW which engine does this have? 4.6, 5.4? Be advised, using cleaners not meant for throttle body cleaning WILL KILL etc throttles. If it stalls at idle, but runs good, it's probably the electronic throttle actuator.
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Monday, June 8th, 2020 AT 5:05 PM (Merged)
Tiny
TCAUSEY
  • MEMBER
  • 7 POSTS
Thanks merlin2021, I'll do what you suggested and let you know the results. It's a 4.6 engine.
Thanks again
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Monday, June 8th, 2020 AT 5:05 PM (Merged)

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