Every time i turn my a/c on my truck the rpm goes up and down

most likely not. look for any vacuum leaks first. if all ok, i would look at the iac motor. it may be bad.

Roy

Where exactly could I look for leaks sorry im not good with engines. Is it in the intake?

yes, along the intake manifold. you may need some help if you are not familiar with this operation

Roy

What would replacing the throttle position do?

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.

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

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.

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.

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

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.

Thanks for the reply, I'll do what you suggested. I think I did just the opposite of what you said. Thanks again

OK keep me posted...

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

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!

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

Is the check engine light on? Autozone can read the codes if any and they do it free, Post all codes found.

No check engine light on. I will go to Autozone to see if any codes come up. Thanks

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

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.

Thanks merlin2021, I'll do what you suggested and let you know the results. It's a 4.6 engine.
Thanks again

OK I will check back!

I work with a Deputy that has a 2005 f-150 5.4 triton v-8 xlt 4wd and is having a problem with his truck shutting off when the wheel is turned all the way to the right and it also done it to him when he stopped immediately. When his truck idles the rpms fluctuate up and down.

Check for vacuum leaks. look at the elbow for the PCV valve. They like to turn to mush.

Good luck and let us know. :)

I'm having the same problem after changing out the battery. My mechanic said he needs to download the new codes to the computer. I didn't try replacing the battery cables in the reverse order.. will try that.

I believe that year has a idle control sensor... i would guess that is his problem...

Two good reads on the subject.
https://www.2carpros.com/first_things/car_surges.htm
https://www.2carpros.com/first_things/car_dies.htm

Let us know. :)

I am hoping someone with vehicle mechanical knowledge can give me some help. I do not know much but am trying to learn. We are on a limited budget so the more repairs I can do myself, the better. My brother knows a good deal about auto repair but he lives about 4 hours from me.

The problem I am having is this. I have a 2003 Ford F-150 V6 manual 2 wheel drive pick-up. When I first start the truck, the idle will go up and down. I think when the idle is steady, it holds at about 1000 rpms. When it revs up and down, it will go a little below 1000 rpm and back up, over and over. When I am driving, I do not notice anything. Once the engine warms up, I think the problem goes away. I can not remember for sure now, but I think this only happens during cold weather. During the summer when the temp was 90+, I do not think it did this. My service engine light is on. This past weekend, we went to see my mother and brother. We went to an AutoZone and they checked the codes. I think there were three codes that showed up. Basically, I was told that it said that my truck was running "lean" (which my brother tried to explain the meaning to me). I was told that the most likely culprit based on the codes and the possible causes given on the print out was that the Bank 1 O2 sensor was bad. One of the possible causes given was a vacuum leak. However, my brother and the person at AutoZone said that if that was the issue, that I should notice more problems than I do. We replaced the O2 sensor. I turned off my check engine light (I disconnected the positive battery cable and turned the key with the clutched pressed - as if trying to start the truck - this will turn off my check engine light). At first, it seemed like this may have helped. The rpms at first seemed as if it was about to do the same thing, but then did not. It may have revved up slightly for a very short duration and then stopped. The next day, when we drove home, however, the same thing started happening again and the light came back on.

I went to another AutoZone and they read the codes again. This time I was told that it was showing the bank 1 and bank 2 O2 sensors. It gave similar possible causes as before. Except this time, the way the person explained it, I am not sure if he said that my truck was running too lean or too rich or sometimes both. He asked what kind of gas I had been running. I told him 87 octane. He said that now that gas has 10% ethanol, that 87 octane is not good for my vehicle and is causing the problem. He also said that it could be that the MAF sensor needs cleaning. After checking my engine, he discovered that I do not have a MAF sensor (to his surprise). He told me to get some MAF cleaner, showed me a plastic tubing piece to disconnect from the throttle body (just have to loosen a screw to a clamp to do this) and to spray the MAF cleaner in this. He said to let this dry for about 30 minutes. Since I have half a tank of 87 gas in my vehicle, he said to add some octane boost to the tank. I called another Autozone for another opinion. He said that I do have a MAF sensor and the other person must have missed it. He said to take it off and clean it and follow the other advice (about the grade of gasoline)

Can anyone give me any insight into this? Any opinions as to what I need to do would be greatly appreciated.

On another note, I know I also need a tune-up. I have put about 80,000 miles on the vehicle (total miles on truck is 103K) and have never had a tune-up. I am not noticing any misfire, however. It does not run "rough". My brother said that he thought that plugs and wires are not probably causing the problem, although he said I still need them replaced. He said that he did not think that needing a tune-up would cause a check engine light to come on unless it was misfiring very badly. I do plan on replacing the plugs and wires but I have to wait until my brother comes to visit this Easter (I am trying to avoid paying Firestone $300 for plugs and wires, when I can buy them at AutoZone for about $60 if done myself).

i had a friend with same problem listen for vacuum leaks we found his under intake plenium area you have 2 elbows rubber that usually get frail and leak 1 by back wall passenger side other by top center front of motor connected to the same plastic tube this leak caused 12 codes.

I have a Ford F-150 4.6 V8. The RPMs has started to surge up and down while driving at a constant speed. If I take it out of overdrive it doesn't surge. It starts fine and no missing. Changed the fuel filter today. No change. I have a K&N air filter. I also cleaned it with their kit. No change.

check fuel pressure and scan for codes. clean throttle plate on both sides with choke cleaner as well as iac hold if you have one.

I took the truck to the ford dealer. They hooked it up and no codes came up. They couldn't find the problem.
I changed out the fuel pump module above the spare tire. This did not help. I drove it a couple miles and the engine died when I pulled into a parking lot. It started right up and I drove it home. It died when I pulled into the driveway. It will restart, but while idling, the rpms will raise and drop by 100-200 rpms. It used to ony surge when i was driving in overdrive at a constant spead.

I haven't tryed cleaning the throttle plate yet, but plan on it over the holidays.

k&n filters can cause problems if they are oied to much so make its not

I have a 2002 F-150, I bought from a guy it's a great truck but having minor issues, this time I am wondering why when I am setting in park the truck is idleing fine but when I turn the heat on my rpm gadge goes up and down turn a/c or heat o of it stops, what would cause that?

This may be a simple as a bad battery connection, remove and clean both battery terminals, if they look corroded replace, terminals must be clean and tight, also check engine and chassis earth points as well.start here.

So I replaced the IAC valve & egr which we dertermind were definatley bad. But after driving the truck for 40 miles it is still idleing rough. It did just set a code but don't know what it is yet. Could it be the MAF? (reguardjng the 2000 F150, 5.4)

First, check to determine what code is set. Also, behind the throttle body, there is a vacuum hose that goes into a 90 degree bend. Check to make sure it isn't dryrotted or broken. It's becoming a common problem.

my idle fluctuates/surges from 750rpm(approx) to 1250 rpm(approx) normal operating temp, I have cleaned the Maf sensor and throttle body - and seems to be particularly hard on fuel (and yes I realize it is a truck lol) other than this the truck runs wonderfully with no hiccups

Clean the idle air control valve and also the EGR and PCV valves, Here is an guide to help you see whats going on.

https://www.2carpros.com/articles/engine-idles-too-high

Please run down this guide and report back.

I had this problem it was a bad PCV hose in the rear of the engine FYI

Have a 2000 F150 idles rough, ocassionally dies at idle. Replaced egr valve & censor, vacuum looks good. What to check next. Says it's too lean.