86 Bronco 5.0 AOD A/C , all the goodies


last week vacuum lines had a melt down on the passenger side exhaust manifold. so i cut out the bad section ( it was a glob of plastic ) and spliced in normal rubber vac hose.

and i did a minor tune up at the same time i.e., plugs, cap, rotor, wires, air filter, pcv filter and pcv valve.

here's the problem. when i hooked up the new pcv valve, it kills the engine at idle. i can give it throttle and it does fine, but as soon as i release throttle, the engine dies. if i unplug the pcv valve, the engine idles fine and it does ok, with a hint of a very slight rough idle.

if i plug in the old pcv, the some problem occurs. funny though, it never had the problem prior to vacuum melt down.

i've check and double checked to make sure vacuum hoses are proper and i don't see any problem them.

any insight to why a pcv value would cause and engine to die at idle? i mean, it won't even hold a few seconds of idle.

thanks,

ambrose

 

Is this an EFI engine or carb?

 

steve, it's EFI ...

in the meantime. i checked timing and it was out about 5 degrees. reset timing to 10 as spec, cleared codes, disconnected battery for about 15 minutes to let processor clear it's memory

hooked everything back up, let the system relearn it's strategy and it worked. found the idle a tad slow @400 rpm, so bumped it up to 600 rpm.

the only thing i can figure it this whole vacuum melt down was a progressive fault. as it got worse the eec adjusted for it and i never noticed, though i did think that power was slightly off. but i took the power drainage as typical with a 100k 302.

damn thing runs like a champ/

i'm was so happy again, i went ahead and replaced my old trusty and rusty tailgate with a brand new shell. ha, now the t/g window motor doesn't work ...LOL

just like plumbing a house

ambrose

thanks for the support sometimes it's just good to talk about it

 

How? The IAC controls the idle, and if it's blocked with deposits, it's best to just replace it. Cleaning it only lasts a little while, so get a lifetime part from anywhere BUT the "zone" .

Have you looked thru these tailgate pics?

 

How? The IAC controls the idle,

there's a nifty little idle adjustment screw ( just like a carb ) above the ics and just below the accel cable linkage and pivot. works real well

and you're right, it's been over a 100 k on the ics. so i should replace it .

thanks

ambrose

 

You're never supposed to adjust that screw. It's set at the factory to prevent run-on and to make the IAC stay in its operating range. By setting the idle with that screw, you've effectively eliminated the IAC from the truck. To reset it, unplug the IAC and back the screw out JUST until the engine dies. If you try to restart it, the engine should run for 1-3 seconds before dying.

 

with all due respect for your great knowledge of ford systems, steve, but with 330,000 miles on my bronco, i see no problem.

as it stands, all this is, is a fast idle screw. it is not an air/fuel mixture adjustment. and in the greater scheme of things, and 1/8 or 1/4 turn isn't hurting a thing. all it's doing is pushing the accelerator cable to a more sightly depressed seating at idle. unless that causes the eec to go ditzy, then no foul, no harm.

in the mean time as you suggested earlier, the ics is most likely dirty and cleaning is futile except for the short haul. when i replace the ics, and i feel the ilde is too high, then i will turn it back down.

but for right now, i like my 600 RPM

thanks for all your help, steve!

ambrose

ps .. if it isn't supposed to be turned then why is it there? seems obvious to me.
if you recall years ago, Ford tried the same thing with carb air/fuel mixture screws by clipping on limiting caps. didn't help much then either.

 

It's not a "fast idle" screw, it's a "throttle stop" screw, which is a TOTALLY different function. If you don't want to reset it, OK. It's your truck.

There are PLENTY of screws on the truck that you're not supposed to adjust. If you had too much exhaust backpressure, would you loosen the head bolts to bring it down? If you weren't supposed to do that, why would they be there? (I'm exaggerating for effect, but the principle is the same.)

 

I have to agree with steve 83. I fooled around with that screw one time, and screwed everything up. I was days getting everything figured out.

Zanny

 

My understanding of it you are both right. Under normal circumstances that screw should not, and shouldn't have to be adjusted as the iac does most of the idle control. But when things start getting old and clogged like ambrose pointed out, the iac may not be able to let enough air past to get the idle up to where it shuold be. So, he let a little more in himself by adjusting the screw. The proper way to fix it would be a new IAC but he basically put a band aid on it for now. Eventually the iac will clog and stick completely and he will have to replace it at that point.

 

I'll third Steve's notion that adjusting the idle stop screw is a wholesale bad idea. I finally realized after replacing a dead IAC solenoid and valve assmebly that some one had run that screw so far in that when the IAC finally DID work correctly my idle was sitting just above 1200 rpm IN GEAR. Thats enough to get you through first gear and up to about 15 mph if you let it go. Talk about wasted fuel and energy. I have no idea how long the IAC was bad but the difference in performance and MPG were more than noticable once I ran that screw back down to where it needed to be. The only reason its a screw in the first place is because of the tiny differences in throttle bores and throttle plate machining processes that make an adjustable stop necessary for initial setup at the factory. All that screw is supposed to do is keep the throttle plates from snapping completely shut when you let off the accelerator. And its function is really to keep the plates from getting stuck in the throttle bores NOT control idle air flow. Thats what the IAC does...allows air to bypass the throttle plates and keep the engine running at idle. If you look closely at the throttle plates themselves, you will also notice that there is a tiny diameter hole in each one about a quarter inch from the shaft. Fail-safe holes should the IAC become completely inoperable....like mine did. Still lets a small amount of air through but not enough to really let the engine do much more than barely lope at idle.

In short, fix idle problems the right way the first time and you won't have to mess with an adjustment that has absolutely NO specifications listed for it. ('cause its not supposed to be adjusted!)