Hi Everyone, I am a newbie poster but long time reader.

History: I have a 2002 F-150 with the 5.4 in it. I bought it with 150K km on it and it is now at 172K. Using the information on this site I was able to change the plugs, clean the MAF, and the throttle body including the IAC. I did this as I was not sure when the previous owner had last had it done, plus it was idling a little rough (felt like it was missing). It no longer feels like it is missing but I still think it has the following problems.

Problem:
1. Since I have owned the truck, it has always had a high idle (surges from 1000 to 1200 rpm) and I thought cleaning the IAC would help. The truck still idles at 1000+ rpm after having the IAC cleaned. 1000-1200 rpm seems high to me, I thought it should be around 700-750 just like the 5.0 in my 1989?

2. Also when starting it whether it is cold or hot, it revs up to 2000+ rpm and takes a good 6-8 seconds to settle down to it's normal 1000 rpm. I thought this would be normal when it is cold, but when the engine is hot it still does this. I thought that when it is warm it would just start and idle at 1000.
My friend bought a 2002 dodge with the 5.9L and his does not go through the high idle on startup like mine, and neither does my brothers chevy 6.0L

I think I may need a new IAC (since that controls the idle) or MAF sensor but wanted to get advice from members of the board that have had a similar problem or have more technical knowledge of the 5.4L.

I was thinking about buying a programmer for it but want to get it running like a top before then.

Thanks in advance for any help/advice, I really appreciate it.

 

I had a high idle on my 01 due to the IAC being gummed up. It had similar symptoms to what you described. One result of the high idle was that I could "idle" down the street at 20-25 mph. Does the high idle continue when it's in gear?

Cleaning the IAC took care of the high idle condition. Unfortunately cleaning was only a temporary fix as the high idle condition started returning after 3 weeks. Replacing the IAC resolved the problem.

 

Thanks for the reply Pilot10. That reconfirms what I thought was the problem.

The high idle does continue for me while I am in gear. It does allow you to idle along at around 30-40 km/h. The problem I have is when pulling my 27 foot holiday trailer it is harder on the brakes.

Do you mind me asking where you got your new IAC from (dealer or parts store)and how much it costed?

 

They are usually under $50. Aftermarket ones work fine. Possibly the previous owner has manually opened the throttle stop screw and the TB blade is not closing far enough?
Does it idle at all if you unplug the IAC?

 

Thanks LXMan1

I didn't think to try and run it with the IAC unplugged. I will definitely try that tonight and let you know what happens. If it continues to run, would that mean that the IAC is toast?

I also didn't know that there is a stop screw for the throttle body. I will also look for that tonight.

Looks like I learned something new today, that is why I love this site.

 

Try this. Back off the stop screw until it isn't touching the throttle linkage. Then run it back in until it just touches it. Then turn it in a little bit more until the throttle just starts to move. See how the idle is then.

 

Didn't get a chance to try anything last night as I got held up running errands in the city after work. By the time I got home and ate it was getting dark and starting to rain off and on.

I have lined up my buddy's garage for tonight so I can get it in somewhere that I can work on it.

LXMan1, I will aslo try your idea of adjusting the throttle body valve adjustment screw.

Will update you tomorrow on my findings.


Thanks

 

OK I unplugged the IAC last night and started the truck. It started and immediately idled at 700rpm. It did not go into it's normal high idle at all. I have never heard my truck idle this low (unless in gear) and it sure sounded nice.
Does that mean that the IAC is toast? What would happen if I left it unplugged, would the engine stall when letting off the gas while driving or have problems idling from a cold start??

While it was running I plugged the IAC back in (to see what it would do). As soon as I did this, the idle jumped up to 2000 rpm and then slowly worked it's way down to 1000rpm.

I was able to find the throttle body bolt that LXMan1 is talking about. It was adjusted to about 1/2 way out. While it was now idling at 1000 rpm, I turned the bolt in and it seemed to cause it to slightly alter the idle down to about 900rpm.

I didn't want to keep adjusting it further as I am not sure if I should replace the IAC and just leave the TB adjusting bolt as is.

Please let me know what you think, I can't wait to get it fixed.

Thanks in advance for any help.