I have a 90 f150 w/ a 302 in it i just got it and tryin to get it running tip top but i found the yellow hose that runs that was loose to my acv and i looked at the lil diagram on the truck but nothin helped me out there. and also my i dont know what it is called but it is behind the manifold and it has what looks like maybe an inch hose hooks up to it but naturally it is gone as well. but i believe that would run up to the canister that is right behind my battery. the truck runs a lil rough when it is cold idles up and down till it warms up the idle spped sensor is unpluged at the front of the engine i took it off and sprayed the inside to clean it up and same thing it will idle at 12-1500 when pluged in and unplugged it runs @ 800-1000. I payed 750 bux for it 4x4 5spd 302 extended cab w/ headers on it. everything works on it i drove it home. just needs a lil tlc thank you in advance for the help

 

It could be several things. Things to try are; Pull the IAC, little thing under the TB with a plug, If I remember correctly you can pull the servo and run a rag though the passages. Go ahead and remove the throttle body, crap builds up behind the butterfly plates and can cause a hunting idle. Replace the EGR valve and tube.

 

Sounds like a vacuum line . Is this yellow thing a small diameter plastic tube about 3/16 inch diameter?

 

yes it is a lil yellow tube about 3/16 diameter

 

I have an 88 F150 with the 300 I6 and I had a similar problem.The hard plastic yellow line was broken at the manifold I traced it to some vaccum solenoid on the drivers side rear of the head.You may have something similar.I didn't trace the lines to see if it was for the EGR or whatever but hope that helps you some.

Oh and where mine was broken I just got some vac. line from autozone and re ran it using the end from the broken line.

 

Sounds like the vacuum line goes to the thermal air diverter valve or (ACV) at the back of the engine. The vacuum for this tube is controlled by a solenoid (TAD) The large hose that is missing feeds air from the air pump to either the back of the heads or to the catalytic converter. The computer will control this operation thru the solenoid valve. Looks like someone may have removed part of the smog controls. The plastic tubes can be replaced with rubber vacuum lines with the same inside diameter.

 

If the TAD was just left uncapped after the diverter was removed, this would probably cause the fast/erratic idle when cold. The TAD valve switches the diverter valve to put fresh air into the first converter (via the heads on the 5.0) until the engine warms. Then, when the engine is warm, the TAD solenoid is shut off, and it diverts the air to to cat #2. If the diverter valve has been removed and the heads plugged, more than likely the cats are gone too (you said it had headers). Sounds like the PO omitted one step in his smog gear removal by not capping off the TAD solenoid valve. Are the headers long tube or shorties?

It also sounds like someone possibly adjusted the throttle stop screw to make it idle at the right RPM with the IAC disconnected. The IAC is particularly useful on the manual trannies since you drop the engine RPM between every shift. The IAC keeps the RPM from collapsing too fast and stalling the engine. Another reason for the IAC is to prevent extreme vacuum in the intake when the throttle is released and the plates close, which will certainly cause an intake gasket failure. The stop screw on the throttle body is NOT for adjusting idle. It's merely for stopping the throttle plates from binding in the venturis. If adjusted right, the throttle plates should be CLOSED, but not binding, and the TPS should read between 0.90 and 1.05 V DC. Otherwise, it will certainly idle fast.

Fast or rough idle is usually a good sign of a vacuum leak somewhere. Check all the little plastic lines first, obviously. Then, there may be a less obvious leak. A propane torch (unlit) will tell you this. if it's idling rough, especially. Stick the nozzle of the torch near the base of the plenum. If the idle smooths, you might wanna have a look at my gallery. I struggled with rough/fast idling and paid a dealership a LOT of money for nothing. I found the plenum leaking, as well as a ton of buildup around the IAC and EGR ports on the plenum, as well as the back of the throttle plates. You may also detect some vacuum leakage around the EGR (unplugged with source line capped), but it should be insignificant unless the EGR is worn out completely. Besides, the EGR should be closed at idle or at WOT.

You'll obviously want to check the timing when you resolve the vacuum leaks and adjustment errors. 10 degrees BTDC with spout removed. Anything higher will probably cause pinging. Anything lower will make it very flat at bottom end.

 

thankx a million i did the propane thing i didnt think about it i was using a rbber hose and the ear trick but found the holes where the smog stuff went to and it was unplugged . the deleted the cats as well hahahaha and i have short headers and no o2 sensor on the exhaust. thank you all for ur help she runs alot better now

 

With no O2 sensor, the EEC will never run as efficiently as it will with one. In your best interest, or at least for increased economy, see if your header on the right bank (passenger side) has a bung for the O2 sensor. If it does, I strongly urge getting one and connecting it. After the engine warms to 195, the EEC shifts from fixed fuel tables to dynamic ones and uses the O2 sensor as a feedback device to let it know how rich the engine is running. At best, it'll try to trim the fuel mix to stoic. At worst (failed or missing O2 sensor), it'll run on the fixed tables, which are generally rich for normal operating. You'll probably start fouling plugs a lot sooner, not to mention, be making the next oil company retiree's pension a lot healthier. No O2, and you may as well put loose money in the bed and drive down the road. If you're not getting a Check Engine Light after the engine gets to operating temperature, it probably isn't there, or is blown. This assumes the PO didn't put a chip mod on it that eliminates the O2 sensor, but I know of none that do. Not that I've shopped for one, either.

If there's no bung, a lot of vendors sell the bungs needed to weld into place on headers. Gotta drill/saw a hole for it, then weld the bung on the header, if not in, then very near the collector on shorty headers. My Ford Racing headers came with a bung on the right bank, right in the collector, and I'm planning on moving my O2 sensor from the crossover in the Y up there, when I have the time to tinker on the truck again. Right now, I just keep it running as close to stock as possible because I don't want weird problems while I'm depending on it for work.