vant

Hello Everyone,

I have an 03 F150 4.6l. After I recently replace my IAC my truck started to have a high idle when I would start or changing gears and a rough idle when stopped or at low MPH. When starting my truck in the morning it will start at 2500RPM's and drop to 1200RPM's and hold. When driving and coming to a complete stop my truck will hold at 1200RPM's and then drop to 600RPM's and fluctuate between 600-1200 RPM's. Truck never stalls and happens all the time. No codes are giving when using a OBDII I have done the following listed below.

IAC replacement
Intake Cleaning
PCV Hose replaced
Tested New MAF and no change (returned new one)
Replace fuel filter
Replaced spark plugs (was overdue)

The only thing that I have read so far is to replace the O2 sensors, Idle Positioning sensor, vacuum leaks, or EGR valve. I am a college student trying to get everything done without going to a mechanic or buying unnecessary parts. Please let me know if anyone know anything or suggestions that I have not listed.

Thanks for all the help,
Brian

white89gt

Does your truck have a tune that is blocking codes from appearing? My truck would throw a code instantly if it was doing what you are describing.

Sounds like a vacuum leak or EGR issue so far, to me.

Wait.... did you replace the PCV valve? What brand did you use?

Jbrew

Bad IAC out of the box....plunger is hanging. You can paint them w/WD40 and manually work the plunger by hand. Most likley all that is needed. You have to actuate it by hand though, once removed...with a little lube. But yea, could be defective, not usually the case. Make sure the number is correct.

vant

No it does not. I just replaced the hose on the back of the intake and throttle body with a generic heat temp graded hose. Just cut it to length and clamped it. Not sure if I am using the wrong terminology.

vant

I did check that today and have done a previous warranty swap with this part and nothing changed. I did what you stated and it did not make a difference. I do not thing the likelihood of me getting two lemons in a row. I will be taking a look this weekend when I do not have work or school and look for other vacuum/hose leaks.

Jbrew

Yea, something is terribly wrong, -have to be missing something...I mean those rpms are up there. You post between 600 -1200 rpms and ONLY after a IAC R&R. If not the IAC, I suspect the PCV assembly is disconnected or not right. Hell there's not too much else it could be. HUGE unmetered air leak somewhere. With the 4six, the IAC is easier to work on, well go over everything again...something your not seeing or hiding from yuh I expect.

white89gt

I was thinking maybe there was something up with the PCV as well. These trucks are very particular to needing Motorcraft only PCV valves too, FYI.

Axios

Sorry wrong thread

MrXLT

Is your transmission or shifting affected? When my throttle position sensor (TPS) was acting up the torque converter would come out of lock intermittently.