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Discussion Starter #1
I have an 85 Bronco 5.0 EFI. It starts right up and runs fine until it's all the way warmed up. Then, the idle will go above normal and drop below normal starting gradually then ending in dying on the low side. When warmed up, it will still start right up and rev over normal but die as the idle drops. It last had a code 31 EGR/EVP. EGR moves and holds vacuum steady and EVP is new and within spec.
 

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I think that is common on the first gen EFI when the throttle body gets gunked up so it passes very little air at idle. Ford sold an air bypass as a retrofit that was installed under the IAC to pass an adjustable amount of air to keep the idle high enough so it would not die before the computer could adjust the IAC. I have used a thicker gasket under the IAC and cut out the gasket between the holes so some air will bypass and raise the idle enough to prevent most of the stalling, however, during the heat of summer mine will occasionally still stall if I don't catch it with the throttle.

Incidentally, 1986 was the first year to have the EFI. I know because I waited to buy mine until the '86 model came out, so how did you get one in '85? You must have had connections.

PS I recently changed out my O2 sensor on my truck for the first time (240k miles) and it improved the idle. I did not even know I had one until Steve and Kos on this forum helped me find it.
 

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Discussion Starter #3
Thanks nelbur, I see yours, at least, goes down the road. With this condition, it won't make it half a block. To get it home is/was: start,(engine revs up)drop in drive, lurch forward, (engine dies), put in neutral and repeat as necessary. It will not take throttle at this point either. The injectors and throttle body were all cleaned. As for the EFI, there are a few 1985 5.0 EFIs on here. (351's were still carbed as you know) The only attraction, lately, to this vehicle is it only has 35K miles...mostly from not starting I'd say...but it runs so well until it warms up!
 

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Can you keep it running by using your foot to keep the idle up? I understood that you had a problem with occasional stalling. It sounds like you have something else going on.

The computer uses the coolant temp. sensor to tell it what temp. the engine is running. It is where the heater hose leaves the top of the engine near the throttle body. I have had several go bad, but usually the engine will not start when warm. It also typically gives a code. Do you have any codes?
 

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My cheat sheet says that code is from an EVP sensor out of limits, which I believe is that sensor on top of your EGR valve. Maybe the valve is open a bit when idling, when it should be closed. Just a guess. I would block off the EGR port into the throttle body to see if that helps your idle, and go from there. Try Googleing "Ford trouble code 31" and see what you can learn.
 

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If you have an 85 302 EFI, :doh0715: then buy a battery operated FORD code reader with diagnostic book which has all the fault codes and explanations for self test KOEO = key on engine off and KOER= key on engine running. I've been using mine for many years with great success and they're available on Amazon for $24.99 just make sure the batteries are fresh and you're good to go instead of guessing, this narrows it down right away....:rockon

Poor idle could be attributed to a vaccum leak in either a plastic or rubber emissions line as they get older they become brittle and crack creating an exhaust leak affecting performance.......www.siliconeintakes.com click on the left "boost/vaccum hose" and scroll around, has an inexpensive initial kit at $54.00 using 4mm, 6mm,8mm and 10mm 6 foot lengths to replace all those old vaccum lines lines that are no longer available anywhere......check out mine at www.supermotors.net/17406 5 from the left....

Good Luck ~ :thumbup
 

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Discussion Starter #8
Thank you. I just use my multimeter for reading the codes. I have one of the code readers but it doesn't work worth a hoot. Normally, a lousy idle could be a vacuum leak but why, only, at a warmed up state? and how would it make the engine rev up and down to a point where it dies on the down side? In my experience, it either made it miss or die right away.
 

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I think this first gen EFI has a bit of an up and down idle when warm, but it will settle in at the right level after a few seconds. However, if the lowest idle is so low it stalls before the computer can figure it out, you have to determine why the low idle is too low. Your code suggests that you have an EGR problem. It may not be related to your idle problem but if it was bleeding some exhaust into the intake at idle it could stall the engine. Typically the soot build up in the throttle body blocks air that normally gets by the edge of the butterflies, slowing the idle enough to cause stalling. Ford issued a retrofit air bleed device that I mentioned above to eliminate the sensitivity to soot build up. There is a throttle stop screw on the throttle body which is factory adjusted and not to be messed with, which may have been messed with, and may need to be corrected. If you check these things and don't find the problem, I suggest you make a AIC bypass gasket like I mentioned in post #2 to see if you can get the low idle fast enough to control the stalling.
 

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Discussion Starter #10
When it's warm it doesn't idle at all. It revs way up and drops the revs until it dies. Occasionally, it will rev way up and then when it's about to die, it will stumble and then rev way up again. This condition doesn't go away. I got a chance to play with it again today. I got it warmed up again and when I was backing it into the drive, I would die and then restart like the timing was way advanced. (or dead battery) and after checking the some other things out, I need to go check the wiring next.
 

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Discussion Starter #11
Well, according to the Diagnosis manual, the problem is either the EGR or the ECM. When really warmed up, the engine didn't want to turn over when restarting as if the timing was way advanced. The EGR has nothing to do with timing so, I bought a new ECM and I'll try that next.
 

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Stalling

I have a 1991 with a 1994 5.8 351w I had a similar issue were it was idle fine that randomly it would drop to about 400 rpm and stay there then as soon as I would give it has it gas it would stall out. I cleaned the throddle body and the IAC sensor wich that helped but then i upped my idle about 5 turns and after about 30 minuets while my computed adjusted it was fine and hasn't stalled sence. That was my fix.it may work even know some things are difrent.
 

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Discussion Starter #15
New IAC a while back, new EGR. Passed codes with 11, but still does the same damn thing. It won't even make it out of the driveway. I think I'll try the throttle body clean up and check the small vacuum ports there in. Thanks guys!
 

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Discussion Starter #16
Cleaned the throttle body and found a cracked vacuum hose today. I got under the truck and found the front pump is pulsing and dying. Voltage stayed at 11+ volts until it started killing the engine and then it would drop below 11 volts. I'm going to replace that pump too and see what happens.
 

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Discussion Starter #19
New plugs, wires, cap, rotor, ICU, ignition sensor, ECU, TPS, IAC, EGR, EVP sensor, MAP sensor, fuel pumps, gas tank, fuel filter, fuel relays,...
 

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Discussion Starter #20
Okay, I checked the connections to the coil and recrimped them. Now, she idles good but doesn't want to take gas when you stab the throttle. Oy!
 
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