I have an 86 F-150 4x2 with a fuel injected 5.0 and AOD trans and California emission equipment. I've only actually driven the truck a few times around the block as it's not currently licensed, but now when I start it up instead of it kicking up to high idle until it reaches operating temperature as it did before now I have to crank on it at least three times before it will start and when it does start it barely idles and wants to die. The idle will fluctuate 4 or 5 hundred RPM until it warms up a bit and then fluctuates just a few hundred RPM. In the engine compartment I can hear a sucking sound but have been unable to locate any kind of vacuum leak anywhere. This truck was given to me by my neighbor because the fuel pumps were bad so consequently I replaced them and it seemed to be fine at that time. Since that time I have done a full and complete tune up including cap, wires, rotor, and plugs. I've replaced the timing chain, water pump, belts, hoses, battery, starter, coolant temp sensor, throttle position sensor, O2 sensor, ignition coil. It even has a new cat on it. I've checked the timing repeated times and it's correct, I've checked the fuel pump pressure and it's within the proper pressure range of about 43 to 45 PSI. I did remove and check the idle air controller and it physically looks fine but could this be the problem? Any help would be extremely appreciated as I'm about ready to throw a match to this thing and be done with it!

 

John, I hate to ask the question, but, are the new sensors Motorcraft? Archion can tell you chapter and verse about aftermarket sensors on one of these. On the sucking sound, are the inlet hoses off the throttle body, if so the IAC makes a huge amount of noise. You might want to try to get a good look at the PCV valve and hose. Unfortunately, you really need a non-OBDII scanner, parts store ones won't work on pre 96 models. A piece of rubber tubing (1/4" works well) can be used like a stethascope to listen for the source of the sucking noise. Good luck with it!

 

Thanks for the info Bill. Unfortunately the sensors are not Motorcraft but Wells replacement parts from Autozone. This problem seemed to mysteriously develop a couple of months ago after it had been sitting in my driveway for an extended period of time, up till that point it was fine, at least when there weren't other problems present. The truck basically just sits in my driveway and once in awhile I go out a start it up just to charge the battery and make sure everything is working properly. I've had this thing for over a year and a half and put a lot of money and time into it. At this moment I can't afford to register it as the prior owner let the tags lapse and didn't non-op it so now it will cost 4 to 5 hundred dollars to get it registered so it just sits. It seems as though this thing is possessed as every time I get ready to list it for sale some problem mysteriously develops and I need to fix it before doing so. I really am at my wits end with this thing!

 

Gee, gotta love the People's Republik of Kalifornia. I'm glad I don't even have emission inspections where I am. Archion and I spent from sometime last year until spring of this year trying to solve his similar problem. If your EGR control soleniods are chattering, it's a good indication the TPS voltage is too high at idle.

 

Here is how to pull computer codes yourself using a test lamp or volt meter:

Ford Fuel Injection » How To Run a Self-Test
Ford Ranger/Bronco II EEC-IV Testing

 

I went home last night and went out and started the truck up. Before doing so I hooked up my fuel pressure tester and a vacuum gauge. Once I got it started it did it's usual barely wanting to run so I increased the RPM until it got up to operating temperature at which time it idled just fine right where it is supposed to. The fuel pressure was between about 36 and 38 PSI at idle, and the manifold vacuum was slightly fluctuating between 17 and 18 inches of vacuum. I sprayed carb cleaner between the throttle body and the intake manifold and around the air idle control valve and the idle and vacuum gauge indicated a slight increase. So my plan is to replace both the throttle body base gasket and the air idle control valve gasket as neither has been replaced and I've removed both more than once but the gaskets weren't destroyed in the process so I just used them again probably to my detriment!

 

It could be anything from the throttle position sensor, the IAC, the throttle positioner (electric dashpot) to the coolant temp sensor, among other things.

You need to do a computer diagnostic.

That and california requires a passing smog test before you can sell a vehicle to a consumer. Unless you get it in writing the vehicle is sold for parts only.

been there done that,

 

Well that's the whole point of this futile operation is to get it to pass the smog check so I can sell it. The problem is I've got too much money into it that I now know I will never recover and therefore don't want to spend anymore money on the dang thing. I've replaced all the components you've listed less the IAC. None of the components actually needed to be replaced but I decided to just as a precautionary measure to hopefully insure it's success at passing the smog test. Yeah welcome to Suckyfornia where you have to watch your wallet constantly otherwise the state will steal it from you. As a native Californian I despise this awful corrupted state government but that's a whole other subject not appropriate for this forum!