I hade all but given up on resolving my rough idle problem when I noticed a few weeks back that when I have the a/c on I don't have the rough idle. As per this site, I have done just about everything possible to at least make it somewhat better with negative results. It has been to 2 dealers with no resolution and no answers. I know alot of others out there have this same issue but have you noticed that having the a/c on fixes it? I have tried to understand how or why this could be possible but now I am looking for some suggestions and opinions here that could finally set me on the right path. Oh, and to beat anyone to the punch, running the a/c all the time is not an option.
Mike

 

I'm guessing that the idle speed is increased enough with the AC on to alleviate the problem. I've got a '97 4.6 with the same rough idle...based on what I've read on this board, I've learned to live with it. It seems like you could spend a ton of $$$ trying to fix it and never get it resolved.

 

Idle speed goes to 600 when the A/C is on in my truck, gets rid of the rough Idle. Mine Idled rougher after I put on my muffler. In park bring your RPM's up to 2000 slowly , notice if you have a shake aroung 1700 or so.