I have an 02 f150 with a 4.6 and yesterday when I started it it would rev up then die so I hooked my scanner up to it and I got a code of p1507 which I assumed was the IAC valve. So I changed the valve and now it revs up to about 2k rpm then drops to about 400 then idles fine around 700 and when I drive it and come to a stop the idle hangs around 1500 for a while then almost stalls then idles fine again. Can anyone make any suggestions to what I should try next? Also I tried hooking my scanner up to it again but it doesn't read any codes.

Thank you

 

Check for vacuum leaks, and did you reset the ECU when you replaced the IAC?

 

Im having a similar problem with my 03 fx4 but the idle only drops when I start the truck warm on a cold start I have no problems im going to check my vacuum lines and was thinking about replacing my IAC but let me know if u solve your problem hopefully it will help me with mine

 

Mine was doing the same thing and just fixed my problem this evening. Check engine light came on couple weeks ago, but didnt notice a problem until this last weekend when it would do exactly what you guys said. Rough idle when I came to a stop or started it up and let it idle. Went to Advance Auto Parts where they ran the codes, for free let me add, and it came back running lean in bank 1 and 2. Said it could be numerous things, but I took it back home to look it over myself and had a friend tell me to check the PCV elbows. He said I am probably have a leak somewhere allowing to much air in. Everything looked fine until I reached back behind the TB and felt the rubber elbow back and it was collapsed and had a hole on the top. It was pretty rotten and falling apart. I assume from the heat on the intake manifold over time. Took a little bit of effort getting it off but bought $7.00 piece of PCV hose and cut a section to replace the old one. Running great and idles perfect now. So I guess I am insisting on you checking those elbows first. I had them coming out of both valve covers. Also since I had the air flow system all off I bought some MAF cleaner and sprayed down the MAF sensor in there and cleaned it up. Never hurts I guess. Good Luck!