Well lets give this "post" stuff a try. I'm new to the forum so bare with me. I bought a 1986 f150,4x2,302 efi,last year. The structure of the truck is in mint condition but the engine and tranny are old and probably ready for replacement. When I bought the truck I noticed that whenever I start it up or come to a stop, the engine will rev very high. Not being to good with auto maintenance I ignored the problem until this Feburary when the truck started to experience even more idle problems. Now whenever I get going the truck runs rough like something is cutting off fuel or air. It will run down the road fine for a little while but you can still fill a little roughness to it. Then when you come to a stop it will die or rev high then low and eventually die if you dont keep your foot on the gas. At the suggestion of a local repair shop I changed the idle air control valve on the side of the throttle body and thoroughly cleaned the throttle body and butterflys. I ran it last night for the first time in about 8 weeks and after 15 minutes it ran good. THEN, when I was a block away from work this morning it started the same old problems again. So far I have changed the IAC valve, fuel filter, air filter, PCV valve, belts and plugs. It has been suggested that I change the EGR valve.?? Any suggestions???

 

Tankerman, may I suggest that you get some codes from the computer first to see what it say's. And if there are some, write em down and disconnect the battery for a minute, hook it up and run truck again until it runs poor. Check again for the codes to see which ones show up. If the same ones appear than they are likely culprits.
If all your tune up parts have been changed than this is the most logical step. At least it will give a better idea.

 

I havent replaced the egr valve yet but I did replace the check valve and tube that is on the back side of the engine connected to both of the heads (the check valve had rusted off). I ran the truck for about 15 miles with no problem, then at a stop light it started surging real bad. The idle went full open then down to choke out stall. Had to keep my foot on the gas to keep it going at a constant idle. It was suggested that I test the computer by using a piece of wire and jumping it to make the emissions light give me the codes? I'll take any and all suggestions. Thanks.

 

You could make a temporary block off gasket out of some thin aluminum flashing or something for the egr valve mount, and see if the problem goes away.

 

I have the same truck and since I bought it in 1997 I have had problems on and off with the idle. One thing I did not see on your list of parts was the Throttle Postition sensor. The truck was my grandfathers before mine and I think we replaced the TPS during one of its stints with idle problems. I think in some other posts either here or on the 302 thread I read that it is subjected to alot of heat where it is located. Hope this helps. Dan

 

I'm going to go with Dan on this one. I had similar problems with a 302. The TPS was the culprit. When they go bad they can cause your timing advance to get out of whack, whether vacum or electronic. This is especially evident at idle. Get the fault codes out of the computer as well. That will give you a good starting point.

 

im in similar trouble myself with a 1986 5.0 302 efi ford bronco.
my intermittent rough engine eventually went to a always rough to wont even start anymore.
One thing I have learned is to now ignore this is the problem just replace this mechanics, most of my efi is now new parts and it still wont even start!
Starting tommorow im never gonna replace a component unless its been tested, even if I have to buy the test equipment!
Getting back to your problem, EGR valve malfunctioning wont cause rough idle unless its leaking control vacumm air into the intake, simply unplug little vacumm line and stuff a bolt in the plastic lines boot, if theres no improvment your EGR is not the problem. Fuel regulator vacumm leaks are similar to EGR leaks but they will also flood the engine with fuel.
Vacumm leaks will cause rough idle but EGR and fuel regulator vacumm leaks are the only ones that will act intermittently.
plugged up fuel delivery system can also cause intermittent rough idle, testing for both pressure at the injector rail and flow volume from the return line will confirm theyre working good.
Since your truck problem is intermittent its should be reasonable to assume after you have performed the above steps that your problem is electrical or electronic sensor related.
A notorious sensor to go bad is the oxygen sensor TEST before replacing, another notorious problem is the TFI ignition module on the side of the distributor, apparently it is heat sensitive.

Seeing as I cant even fix my own truck my advice is probablly bass ackwards anyways sorry.