Generally starts and runs well. Idles a little rough. Was on the highway last weekend and the truck sounded "fut-fut-fut" like it was missing on a cylinder when I stepped on the gas, but it easily held 70. Then later traffic slowed and she had trouble getting up to speed. Got off the highway and she didn't want to rev past 3500. Stopped, cooled down for 10 minutes and she was good again.

I just got an OBD-1 reader and it's pulling code 84 on the Key-On, Engine-Off (KOEO) codes. The book just says EGR (exhaust gas recirculation), but this website http://www.troublecodes.net/ford/ says
<table border="1" width="566"><tbody><tr><td align="center" width="28"><center>84 </center>
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I have the 3 book OEM service manual, but it says there's a separate emissions book I need.

So where to start?

 

Just tested the EGR valve itself. The diaphragm holds vacuum, the valve works - manually putting vacuum on it with a hand pump will vary idle speed and eventually kill the motor. This is good news, as that EGR valve is expensive!

Now need to test the EGR solenoid and the position sensor.