I have a 2001 Fort Explorer Sport 4.0 V6. I have a cold air intake on which has greately improved the performance and gas miledge until about a 1 1/2 years ago. I was getting 18-22 mpg and as high as 23.5 two times and am now getting 14-17 mpg. The acceleration and performance is excellent. When I first start the engine and it is cold the engine will idle at about 1000 rmps and fairly smooth. After the engine is warm the idle first drops to abouty 600 rpms and is very rough, then it drops to 500 rpms and die unless I keep my foot on the accelerator and hold the rpms at 1000. I have replaced the EGC Valve and the Idle Air Control Valve and the Spark Plugs with no improvement. I have thought of reglacing the PCV valve but find it very difficult to get to. Do you have any suggestions as to what my problem could be and what I should do next?

I had the same problem for a while and i just figured out what it was. I had a vacume leak just behind the radiator hose in a small elbow hose. I would check for a vacume leak. I did the same things you did and that was all it was.

I have a vacuum leak in the same location. Is it normal for the radiator hose to rest on this vacuum hose elbow? I wondered if my engine was missing a bracket.

mine sits on it too and from everyone that i've talked to alot of them have been having the same problem with that hose and as far as i know there is no bracket there. The thing is, that hose leak has a tendency to make the engine register that its running lean on both banks I beleive its codes 171 and 174. It was also causing it to read that there was a random missfire and it would only happen when it got warm and it would have idle problems then.