Hello guys! I replaced the IAC on my 2003 F150 with the 5.4l a couple of weeks ago. Since then, the engine will want to die while driving. Sometimes it does completely die, but mostly it will cut out and then come right back. It seems to be happening when I hit a bump, but also when the truck is warm.

So far I have checked the connections to the crankshaft position sensor, ignition switch, and also checked all the vacuum lines and hoses. I am stumped! It is not throwing any codes at all and monitoring the computer with the Forscan app doesn't shed any light on the issue.

Has anyone experienced this before? What else should I check? Thanks in advance!

 

NMI - Did it do this before you replaced it ? Why did you replace it ?

 

It was starting to idle erratically and ended up setting a code for the IAC. I also cleaned the throttle body when replacing the IAC.

 

Did you clean the ports for the iac, i would recomend cleaning the whole entire throttle body, mass airflow sensor, and making sure egr valve is functioninf, yours is doing the same thing that mine sid , i did all those steps and one of them fixed it

 

Thanks... I didn't think of cleaning the EGR valve. I may take the throttle body off and clean it again as well as the EGR valve.

 

Yea you got a bad or sticky IAC. At times a new one may have sticky plunger, hitting the plunger with WD40 and working it by hand may do the trick. You have to remove it to do so.

There's also knock-offs, non Motorcraft units out there that faulty out of the box....regardless, this is IAC.

 

I guess I'll mention this, a little reluctant at the moment but never the less. - Could be EGR, if so, it's non reparable, nothing you can clean without compromising the diaphragm, but yea, you should do this first before removing the IAC. Start it up, let it idle. While at idle remove the green line at the saucer section. Attach your own section of spare hose to the EGR saucer port. Suck on it like your drinking a milk shake until the engine begins to stall. Then stop and the engine should return to normal idle.

If it returns to idle, EGR is good. If it does not or takes awhile to idle normally, then the EGR valve is hanging. If hanging, there's nothing you can do, needs to be replaced. They usually don't go out this way. In most cases when they stick , they stay stuck. These valve only open at cruising speeds and just for a moment, then close right away. Otherwise it will suck too much exhaust and want to stall.

 

Thank you for the advice Jbrew! I just tested the EGR and the engine returned to idle as soon as the suction was released. At this point I am thinking it must be something related to the throttle body since that was the only part I removed. I may remove it today and make sure it is thoroughly cleaned.

 

Like I said then, it's IAC.

 

Just finished removing the throttle body and cleaning everything again. This time I decided to remove and check the PCV hose at the back of the engine; for some reason I neglected to check it last time. Sure enough there was a hole in the tube! I think when I would hit the throttle the engine would suck in a ton of unmetered air, causing the stumble. I also rechecked every vacuum line and so far no issues. I think it may be solved!