Will a bad IAC do this?
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Senior User
Joined: Apr 2003
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Will a bad IAC do this?
A couple of symptoms are: if I don't let the truck sit and idle down when I start it, the engine surges when I put it in gear. And also, when cold, it will not go to "fast idle" but wants to keep stalling out unless you hold the throttle. If it does idle on its own, it will be at only about 500 RPM. If it is the IAC is it a pain to change? Thanks.
Senior User
Joined: Mar 2007
Posts: 403
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From: Medina TN
Yes, an IAC will do that IMO. I have done a 5.4l and a 4.6l and the 5.4 is harder to do. I found it much easier to just take the upper intake off to replace it on the 5.4l. You need to clean your egr ports anyway while it is off. It took me about 1 hr to do it all including cleaning the ports. Good luck.
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Joined: Mar 2007
Posts: 15
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From: Calgary, Alberta, Canada
I had the same problem a month ago. replaced IAC, engine runs a bit better but idle is still rough some time. checked PVC hose & replaced PCV valve, no go. When I opened up the upper intake, I realized how dirty my intake is. a very thick layer of carbon/gum deposit!! After a completely detailing(intake), the engine idle is stable. In your case, could be IAC, PCV, EGR, or a dirty intake. you never know!!
98 F150XLT 4.6 4X4 196000K
98 F150XLT 4.6 4X4 196000K
Senior User
Joined: Mar 2007
Posts: 403
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From: Medina TN
To clean the EGR valve, You just remove it, apply vacuum and run some cleaner through it. To clean the EGR ports in the intake, this requires a little moer time but very little knowledge. The ports are located in the upper intake plenum between the intake and the throttle body. To find them, just follow the path from where the egr mounts to where the exhaust gasses enter the intake. On my 4.6l, they were on the bottom and were hard to see, but boy were they clogged. You have to remove the upper intake to access these ports. Some say to replace the gaskets, some don't, I did not. It took me about 1 hour to do the entire job. That was back in the summer and I have not had the dreaded p401 code to return. Good Luck.
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