Just bought a 1990 F250 with a 93 351 in it. Runs good when on the road or when you rev it but when it idles especially when it's cold it will idle a little rough. It will rev about 100 rpm's and then back down a sputter a little and then back up again. Does a little bit when it's warm but not as bad. When you first start it stays on High idle good but when it comes down it starts doing it up and down thing. Any ideas of what this is???

 

I had it plugged into the computer last night and we figured out it was the EGR Valve Controller. Just thougt i would pass this along.