I've got a 1988 F150 4X4 5.8L with c-6 3 speed auto. It's always idled roughly and is no quite a bit worse than ever before. 74,000 miles on it.
I've changed 02 sensor plugs wires, distributor cap cleaned injectors scanned and found no codes, checked fuel pressure, pulse width to injectors, breakout box check. Everything we could think of.
Found a service bulletin from Ford that says the EEC-IV unit should be replaced with one with newer operating instructions because of rough idle. The only thing is they can't supply the replacement part. There must be someone out there that has a used one or perhaps there is another part number that replaces the one that we can't find. I'm getting pretty tired of trying everything and getting nowhere. Does anyone know where I can get an EEC-IV unit that will work with my engine? I would really appreciate any help you could offer.

Thanks, Ron G.

 

I can't help you with finding the ignition unit, but for one last (cheap) try, do this: Get a can of spray throttle body cleaner, pull the air cleaner hoses off the throttle body, rev the wee out of the motor, and spray the cleaner down the throttle body 'til the can's empty. DO THIS ONLY IF YOU HAVE SPEED DENSITY EFI! My '91 starts to idle progressively rougher, and periodic spray cleaning helps tremendously (278,000 miles does not help).
Ed

 

Ed, Thanks for the hint. I'm not sure if I have the same setup as you mentioned. I've got the two hoses from the air cleaner goin up to the throttle body. It sits atop the big aluminum colored manifold with the tubes. The manifold says Ford Electronic Fuel Injection.
Is that the setup your talking about? Let me know and I'll give it a try.

Thanks again,
Ron

 

Ron,
Think hard about changing out your computer. You can only buy rebuilt units now and they cost about $100 . Actually, unlike the General, Ford computers tend not to fail. Your post did not mention cleaning the by-pass (BYB) valve. It is that part held on to the intake with two bolts and has a three-wire plug on it. Take it apart and clean it with with solvent. Also clean the throttle bore where it mates with the butterfly valve. This is a common cause of idle problems on Fords. When gunk builds up around the butterfly valve the idle air is restricted and the by-pass is overburdened to make up the difference. HTH
Fl Panhandle

 

Yes, Ron, your EFI setup is speed density, spray away. Also, pay attention to post #3 above. Good luck.

 

I worked on my engine yesterday afternoon. I found the by pass valve I believe. Is it the valve on the side of the throttle body? The valve I checked had some kind of sensor or solenoid that worked a plunger. There were two holes, one on each barrel of the throttle body that drew air thru the side of the throttle body thru the valve then behind the butterfly valves. When you first start the engine with the air cleaner hoses off you can hear the air being sucked thru those holes. It's really loud. After about 30 seconds the engine starts to idle down and the air flow through the valve slows down quit a bit. You can stick your finger over the holes inside the barell and feel the suction. I cleaned everything and it seemed to be working fine. I did notice that the butterfly valve was basically shut completely during idle. Tonight I spray throttle body cleaner(alot) and the butterfly valves look as clean as they can be. The thing is still idleing poorly. It seems that the engine has to be at operating temp. for at least 20 minutes before the really rough idle starts. Do you know of anything else I might check? Could an injector be clogged? I see that 4 or 5 of them are easy to get at but you would probably have to remove the intake manifold to get to the ones on the passenger side of the engine. Are they easy to clean? If so how do you remove them? My mechanic did run two bottles of injector cleaner thru the engine @ $11.00 a pop. I also ran some of the cleaner through the holes on the egr valve you could really tell when I sprayed that in. I had to do it under high RPM's or the engine would die. Does that mean anything? You can sure tell I'm not very experienced at this can't you?
I do appreciate everyones help and hope to solve the problem soon.

Thanks again,
Ron G.

 

You have indeed located the bypass valve. The solenoid on the part actual operates a "dither" valve to control the idle by controlling the amount of air allowed pass the butterfly. Problems with the bypass usually manifest as an inability to hold an idle or stalling when the throttle closes (like downshifting when turning - no power steering - look out Ethel). A high idle would more likely be a stuck open bypass which does not seem to be your problem. A long shot may be the temp sensor which regulates the fuel/air mixture, richer when cold and leaner when warm. A vacuum leak will also cause a high idle. Might take a length of plastic tubing and do the Ben Casey routine listening around the intake manifold and vacuum fittings. If there is no missing or surging on acceleration or high speed your injectors are probably OK. Might also check your EGR valve. Don't get discouraged or give in to the commercial technocrats yet. HTH

 

Sorry I haven't answered your post. I haven't done anything new yet but I did notice a kind of surge at slow speeds. It's kind of like when the idle gets rough and the engine wants to die it will all of a sudden rev up a little. I guess the computer compensates at some point and keeps the engine running. I feel like I notice the same thing happening when I drive very slowly at slightly more than idle speed. It also seems to hesitate a little when I accelerate on the road. Is that normal? Thanks for your help.

Ron G.

 

In your prevoius posts,you mentioned you were goin' to SPRAY the throttle flaps.That's ok,but,you really need to SCRUB them, as well as the bores. An old tooth brush and some solvent will remove the gum and sludge that just spraying won't get at. No need to scrub deep past the flaps 'cause you'll never get all that sludge out,so don't bother it.Pay close attention to the area where the throttle shaft passes through the body,clean VERY good.I can promise you,you won't be wastein' your time here.
Phillip

 

Thanks for the quick reply. I'll give it a try right away. By the way, do you remove anything or do you do it right where it sits?

Thanks again,
Ron

 

Simply remove the fresh air snorkel hose at the throttle body & the air filter box.Then get busy with a brush & solvent.You can hold the flaps open by hand or a bungy cord.You can also remove the air bypass solenoid & valve body for a more thorough cleaning,but you may need a new valve gasket so get one just in case you tear the original one.The solenoid uses an o-ring which won't get damaged if you twist first,then pull back.Good luck.
Phillip

 

Thanks again for the help. Do you recommend any certain kind of solvent? Would you use something like brake cleaner? I'll give it a try when I hear back from you.
Ron

 

Yes Ron, brake cleaner will be sufficient,if that's what you have already. Electro-clean, throttle body cleaner as well as carb cleaner can be used as well.I have seen previous warnings from someone on this board about teflon coatings in throttle body's, but I didn't see any of that on my 88 F150,just plain old cast aluminum that is machined.I'm sure there are certain other makes & models that do use such coatings,but staying away from carb cleaner ought to be safe enough.It will be a little tough to get the engine started after the cleaning because of vapors,but it will start,just be prepared to push the pedal to prevent stalling initially,then juice the pedal a few times to clear off any vapors left,then test drive right away so as to bring up the engine temp & reset the idle. BTW,there is a manual adjustment for the throttle stop,it's the screw without a normal head near the throttle shaft.If totally necessary, turn it with pliers to adjust to open/close the flaps.
Phillip

 

Phillip,

Thanks for the prompt response. Do you think it is possible that the flaps could have been set wrong from the very beginning? It looks to me like they are completely shut at idle speed with the only air available to the engine coming thru the bypass. Another question, How can you be sure the EGR valve is working properly?

Thanks again, Ron G.