I recently had a fluctuating idle on my 03 s-crew, 4.6L. I took off the EGR and IAC valves and inspected and cleaned them as best I could. I ended up buying a new IAC valve ($150 at Ford!!!) and after I put it on, I had the same idle problem. Out of dumb luck, I reached behind the turn down elbow behind the throttle body and found a hole as big as my finger in the 90 degree elbow of the rubber pcv line where it attaches behind the throttle body. Over the years, heat and vacuum deteriorated this thing to the point that it fell apart (see picture). When I plugged the hole with my finger, the truck returned to normal idle. Figures. Oh well, a least I have a new IAC valve. Getting the rotted hose off the connection behind the throttle body defines the phrase son-of-a-b@#*h. Prepare to have your hands look like you just finished a UFC title fight when your done. Anyway, this is a hard plastic line joined to the valve cover and the throttle body by rubber elbows. To find a replacement, the elbow has to be stiff as this line pulls a lot of vacuum. I will probably replace the whole set up with a long piece of thick walled rubber hose as I can't find the correct elbow. Checker didn't even have it listed in their parts book. Anyway, I hope this saves someone $150.

 

Good write up and excellent pics.

 

Dude.. you saved me lots of money.. I had the same identical symptoms you listed.. replaced the IAC with no luck.. crack in the PCV elbow was the problem. I found a similar elbow in the HELP! section at my local parts store .. part number was 47028. Worked like a charm.

thanks for the post.

 

I have a 03 ford f150 4.6 trtion 2wd 2valve when its in park the idel goes up and down and it wants to keep loading up also when im driving it if I keep it at 2000 pm it drive fine till its coast then its like its jumping some also when I come to a red light and stop it wants to idel up and down and down to 4 or 500 rpm and cuts off but cranks back up I checked all the hoses and changed egr valve and the pvc valve i took out cleaned and it rattles when i shake it I took intake off 2 times to make sure nun was pinched or broke i am truly stumped please help also all of the injectors and coils are firing right