I see So many posts in the Engine forum about IAC's. I know it's not a major fix, or a lot of money. But What is it about them, that causes them to clogg up after about 50K Miles?

Just normal Dirt and Driving? Or is there some kind of Defect?

 

These trucks just seem to have a problem with carbon build up in them and throughout the whole EGR system.

A cheap can of brake cleaner to clean them out takes care of the problem though. Nothing majores.

 

Yeah, these engines just have a tendency to let alot of carbon get into the intake system, hence why the EGR valves and IAC's get clogged with crap.

 

HI!... You just need to have a heavy foot all the time like me. The carbon never has time to build up!!!

 

The closed crank case ventilation also causes oil to mix with the carbon and cause heavey surface accumulation right in that area.
All Ford EFI systems from 85 up have the same problems because the basic design has not changed.
The Feds mandate the crank case never be open to the outside so this has to be the only way to handle it.
The differences in engine ring seal, valve stem seals, how the engine is driven, winter driving, maintance and even oil type can all influence this problem over a given time span.

 

Seems like some trucks have a problem and others have no problems. We have two late model F-150's both with 5.4 engines - one is a 1999 with 80,000 miles and the other is a 2001 with 98,000 miles. Both were purchased new and neither has ever had a problem with any sort of carbon build-up.

I wonder if the difference is that our trucks seldom make short trips. We live about 25 miles from the city and although they see lots of dirt roads daily, once they are started it is always 30 minutes to the next little town before they might have to stop at the post office. We are not particularly lead-footed, but the trucks commonly run over 80 mph on the interstates around here.

Otherwise, we use mid-grade gasoline, keep the oil changed every 3,000 miles, air filters and fuel filters are changed frequently - otherwise they are maintained faithfully by Ford's maintenance schedule at a good dealer. The trucks have no modifications from stock, have been virtually trouble-free and both literally run like new.

I don't understand it either and glad we don't have the problem.

 

Whats an IAC?

 

Idle Air Control valve. To control the speed of the engine at idle. This from the manual:

The idle air control (IAC) valve assembly (Figure 126), (Figure 127) and (Figure 128) controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.

The PCM uses the IAC valve assembly to control:


l No touch start

l Cold engine fast idle for rapid warm-up

l Idle (corrects for engine load)

l Stumble or stalling on deceleration (provides a dashpot function)

l Over-temperature idle boost.

l Air Assist to Injectors.

 

Funny that i asked what it was. Ive been having an idle problem with my truck. It doesnt idle very steadily. It goes back and forth between 100-200 rpms at idle. Is this a good example to determine the time to change the iac?

Thanks

 

you mean 1000-2000?

[QUOTE=norrisboat]It goes back and forth between 100-200 rpms at idle. /QUOTE]

 

[QUOTE=Van Flicke]you mean 1000-2000?


I think he meant that it bounced in a 100-200 rpm range at idle. Say 700-900 rpms.

 

Its 100-200rpms for mine.

 

Yoyr truck idles at 100-200rpms?

 

Before I replaced my IAC My truck would shudder to stay on at around 100-300 RPMS Until I tapped the IAC with a screwdriver or something.

Yeah, Norris. Sounds like you need to replace it, just hope it's not your fuel pump

 

My truck would shudder @ 500 rpms, I can not imagine one of these motors running at 100rps.