I recently installed and AFE intake for my truck and throttle body spacer. I noticed a really loud and annoying sound coming from the intake and determined it to be the idle air control valve. I have heard they are a common problem on the 4.6L. I replaced the valve and still having the same issue and it will not idle right. It will drop to the bottom of the rpm range and then want to stay at an idle at about 1500rpm. I can't get it to quit acting up. I did once and it lasted about a week and I have no idea what I did to fix it so I cannot duplicate it. would a idle air "restrictor plate" work to limit the air flow and maybe not cause so much air to flow and have the valve constantly over-compensating for the amount of air? Any help will be appreciated.

 

I would also take a look at replacing or cleaning your EGR. Common for the ports to get built up in the 4.6. If that does not work:

Put your stock intake back on and get rid of the throttle body space. Unplug your battery for 30 minutes, the re-attach it.

Drive for 50 miles.

Come back and tell us if you still have the issue.

 

Mine does the same thing but its a 5.4 and tackle you told me a while back to clean the egr I did and that's when it started. Should I replace it?