I pulled my IAC yesterday to clean it. It was not too bad a shape and cleaned easily but I found before and after I cleaned it I could blow through the lower hole and have it come out the top one, not much but I figure enough to cause an Idle problem. If I remove the solinoid it doesn't do it so I put the solinoid back on and as I tightened it up I could see the valve rod being pushed ever so slightly to open the valve. My question is, should the valve be completely closed when there is no power to the solinoid or is it supposed to by-pass a little? I don't think it should. Perhaps the valve is worn. If I were to file a bit off the tip of the valve pushrod the valve would remain closed until the solinoid opens it. I do not have another IAC to compare it to so I am relying on the people on this forum for answers.Please advise. SR.

 

A quick and dirty way to check the IAC is unplugg it while the truck is idleing. The vehicle should die.. Not sure about the valve being completely closed though, sorry.

 

I did try this and the truck ran rough but stsyed running. When I hooked up the wires it went back to a fairly stable idle. It has allways idled a bit rough though inspite of new wires plugs cap and rotor and fuel filter and regulator (warranty).

 

steveray, you didn't say what year you had, so I will try to generalize this for you, it sounds as if you have an upper intake plenum leak, (if it is a v-8) or a vacuum leak(if it is a straight six). From what I see on my Snap-On scanner for 90 an later is the IAC is working at least 20% of the time, so it never is totally closed. Now the pulling off of the wiring is a good and valid test most of the time, and when it is idling rough and also running after you pull the wire connector off the IAC, it is most of the time a vacuum leak some place in the induction system. Now the best way that I have found, (and by the way this was not tought to me by Ford). get your hands on a averaging dc voltmeter, put the meter in dc volts, and measuring 14 volts. Put negative lead to battery negative, take red lead and backprobe with a sewing needle into the white wire at the IAc motor. Start the vehicle, let the engine run alittle until at lowest rpm idling, numbers on the dc voltmeter should be 9.5-10.5 vdc.
If the numbers are higher than this, the iac is not working hard enough, or there is air leaking around some place other than the throttle plates or IAC motor ports. If the numbers are lower than 9.5 then the iac is working to hard, then you need to check for carbon buildup in the throttle plates and IAC motor. It would also be a good idea to first check that the Throttle Position Sensor is calibrated correctly, which it is the center wire with the key on engine off to be .95vdc, no higher than .99vdc. This is critical. Then check IAC motor duty cycle with the dc voltmeter. Another point is also, if the numbers on the IAC are lower than 9.5 after you clean the carbon out of the Throttle plate and IAC, your RPM's need to be raised up. This makes the IAC work easier also, which give higher numbers. Hope I didn't get to deep, but this works for ALL FORD vehicles, not just the trucks. Electric1

 

Hey, a freind of mine recomended me to this site bc I have a problem with my 95 F-150 w/ the 4.9L I6 and a 5-speed. I think my IAC may be the problem. I was wondering the symptoms of a over/under worked IAC would be. My truck bucks something fierce in low-mid RPMs and just boggs other times in the same RPM rage. base model with no tack, so i dont know actual numbers. any help would be greatly appreciated.

 

Unplug the EGR and re test drive the vehicle, Ford has a big problem and always has with the EGR. Also found that there is a vent hole in the throttle plate that is there to compensate for air around the plate to make idle correctly, In due time the throttle bore gets wear beside the plates and that hole is like a vacuum leak, I solder up the hole and the buck has gone away also, have done this twice with success. Hope this helps. Electric1

 

Electric1 , Where is this vent hole on the throttle plate & what engine , throttle body are you referring to ?

 

I just sprayed some cleaner in mine the other day and it helped the idle problem but not the throttle lag off idle. There also seems to be a lean surge at cruise at low throttle. The hole the previous message was about is interesting to me. There is a hole in each of the throttle butterflys and I am assuming that this is the ones he is refering to. I also noticed that there is an ajustment for the throttle buterflies under the plastic linkage cover. Would backing this ajustment off a bit return the butterflies to original settings? When new are the butterflies fully closed or partly open. I would think that they would be just a bit off of fully closed to prevent them from sticking in the closed position. Any thoughts? SR.

 

Question for y'all - I'm up with, and in the midst of, creating a restrictor plate for my 4.9's EGR, but where is the IAC on my 1993 4.9?

I know you guys can answer this, so thanks in advance!

Dave

 

Dave , Its located on top of the upper intake , just past the throttle body . The whole assembly is about 8 in long , It has a two wire connecter , part of it is round on one end & its solenoid is on the other end .

 

merci Big Paul.

I'll have to get after that part, take it apart (or off) and clean it soon.

 

Sorry Paul and stevieray, was away for awhile, the holes that I am refering to, stevieray was correct on finding, they are in the center of the throttle plates, What I found was common on this 4.9 engine was that Ford set the clearance very tight for the throttle plate to throttle bore area, which then as air or dirty air even with an air filter in the box, the carbon blowback and air would wear the throttle bore and plate area wider or made the measurement bigger, allowing more air to bypass the throttle plates and not go through the IAC as Ford wants it to, what I also found was that on Data it would show 20% duty cycle on the IAC control, which at 20% the IAC is completely closed, now if you only solder the holes shut in the throttle plates, it made the number go to 35-37% duty cycle which is a functioning Data number for Ford computer function, which now that the wear is in place and you solder the holes shut, you should not have that problem again, I have not seen a single Ford 4.9 back in my shop for this problem since, now as far as the turning of the throttle screw you saw Stevieray, I would suggest staying away from it. But if you have to touch it, let me know and I will explain my own found true to life procedure that works every time, step for step what Ford doesn't think you need to know.
Electric1

 

Thanks for the reply 'lectric. My problems seem to have gone away so I am not going to tinker with the scew. The truck is running fine now and the only problem I have is with what seems like the clutch is not fully disengageing makeing it hard to get into gear. It is a new clutch and pressure plate so I think it may have something to do with the master/slave cylinder but it is too dang cold to be messing with it right now. Whe it wearms up I will try bleeding the hydraulics to see if that helps.

 

Hey, Electric1. I just cleaned my valve train and put on new intake gaskets and seals (including lower/upper gasket, throttle body and IAC gaskets and EGR gasket). Also cleaned the Throttle body and idle air bypass ports. They are spotless clean. Engine now idles rough and higher, even when warm. About 1000 rpm and starts like a cold start every time with high initial idle until the IAC trys to lower it. Disconnecting the IAC does not change the idle. I tried lowering with idle set screw but does not do much and still idles rough. I counted the turns on the screw so I can go back to original setting. What was your "tried and true" method of setting up proper idle speed after this kind of work has been done. I have done a manual reset with a mazda but after much adjusting of base idle and TPS and trial and error. The other thing is the sticker on the throttle body that says not to clean it (it was really gunked up on the intake side, and so was the IAC). Any information would be really appreciated.

 

kwing, I'll try to keep it short as possible, unhook battery cables and clean, reinstall cables on battery, you need an averaging digital voltmeter, K.O.E.O. (key on engine off) place voltmeter into dc scale, place black lead to battery negative and red lead to center wire of T.P.S. sensor, ( I believe it is the green wire), and you need to read .95 volts DC. if higher than that, turn idle screw out to bring down numbers, if the throttle plate gets sticky inside throttle bore, then set throttle plate at point of no stick, remove TPS sensor from side of throttle bore, wallow out the T.P.S. sensor mounting holes to get the sensor to adjust to .95 volts DC, once you have the throttle plate set, then take the red probe and backprobe into the white line of the IAC valve assembly, set voltmeter into DC averaging range, start vehicle, DC voltage needs to average between 9.0-10.5 volts DC, if the numbers are higher than 10.5 then you have a vacuum leak somewhere, if the numbers are lower than 9.0 turn the throttle adjusting screw in to make the throttle plates open wider and let in more air, letting the IAC valve work less, hence higher averaging numbers on white IAC line, I suspect you have a vacuum leak somewhere, start engine, unhook EGR and place finger over the EGR pipe hookup port at EGR and feel for a vacuum leak,if you hear RPM change, clean EGR assembly with propane torch and blow gun, use vacuum pump to open EGR valve and hold open to clean out carbon, unplug PCV from valve cover, put something over the PCV itself so to stop vacuum leak into manifold, spray carb. cleaner into valve cover at oil fill hole and listen for engine rpm change, if it changes, your interior manifold gasket has a problem, if not move on, spray carb. cleaner on exterior of base of plenum at the upper intake, listen for RPM change, if RPM changes, look at that area for the problem, I hope this helps you find you problem, Electric1