Since it took me over a year to figure out the problem, I thought I would make a post to potentially help others with the same problem.

I have a 2004 6.0. I love the truck, and I take very good care of it. A couple of years ago, I noticed RPM's would drop periodically while idling. This was more regular if I had been driving for a while then stopped at a light. It wasn't a big deal, but it annoyed me, and I like everything to be "right". There were no lights on, and no codes.

My searches indicated that it was likely an ICP sensor. I replaced it, and I *thought* it got better. But it was such an intermittent problem, that was hard to say for sure. However, it didn't take too long before it started happening again. I started digging back into it, and I read that it's common for Amazon items (which is where I ordered it) labeled as OEM to be fakes (I am strict about only buying OEM). So, I ordered a real ICP from the dealer and replaced it again. Same story. Seemed to be better but then the problem came back. I really had kind of given up on it, since it wasn't a real problem. But then, the symptoms got worse. Sometimes the RPM's would drop, but sometimes it would surge. If I wasn't pressing the brake hard enough, it would actually go forward. Sometimes when I would try to go forward from idle, I had no throttle response. It would just sit there. A couple of times it even died when I would stop at a light or even just slow way down. However, it would be "fixed" after shutting it down and starting it back up. At this point, it's dangerous and must be resolved. So the search continues.

Somewhere buried deep in some ancient thread somewhere, I found a guy mention something similar happened to him, and he kept taking it to shops, and they never could figure it out. He took it to a dealer, and they couldn't find anything based on the computer, but they replaced the ICP and IPR valve as a guess, and he said it fixed the problem. So, I ordered the (very expensive) IPR valve and said a lot of profanities installing it (it's a major, major pain). This was about 2 months ago, and the truck has run perfectly ever since. So, I think I can say problem solved. The IPR was the problem.

So to summarize...
Symptoms: Rough idle, dropping RPM's at idle, surging at idle. no throttle response after idle, engine dying at idle or very low RPM's.
Solution: Bad IPR valve (injection pressure regulator valve)

Now that I understand what the ICP and IPR do, it all makes perfect sense, but at the time, it was very frustrating. I hope this helps someone going through the same thing.

 

Glad the truck is doing well. Only one thing to "nudge" you on ................

The sensor is ICP, not IPC.

 

Oops. Thanks for pointing it out. I have fixed the original post.

 

LOL - no big deal at all. Not like it isn't fairly common!

 

Thank you for taking the time to post this and especially for including the details. These threads are always better when a final solution is reported. No doubt this will help others in the future.

 

So was the problem the ICP or the IPR cause the original post still says IPR.

 

 

My IPR valve has been replaced but not the ICP. Whenever I start the truck cold it idles rough like its cammed and suffocating for air. I opened the air box up and it gets a little better but still not great. It gets better as the truck comes to normal temperature but still isn't 100%. Would the ICP sensor be my next go to or should I try changing fuel filters first? Its a 2004 F350 Super Duty

 

To test that, simply unplug the ICP sensor and do a test drive.

And how many miles are on your current fuel filters?
When was the last time the water was drained at the primary fuel filter (HFCM) drain plug?
What is your fuel tank level?

Do you have a scan tool?

 

Do you have a fuel pressure monitor?