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post #1 of (permalink) Old 12-11-1999, 06:56 PM
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Rough Idle

My 86 Bronco XLT 5.0 has a rough idle when warm. It stays rough until I get up to about 10 mph, then it kicks in and runs fine. I just put new plugs cap rotor and wire and also timed it. Could it be in the fuel injection? It almost wants to stall but does not. Also it surges at idle. Any help would be appreciated.

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post #2 of (permalink) Old 12-12-1999, 12:37 AM
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Re: Rough Idle

Did the idle problem begin after the tune up work?

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post #3 of (permalink) Old 12-12-1999, 11:59 AM
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Re: Rough Idle

The problem started before I tuned it up. Thought the tune up would help.

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post #4 of (permalink) Old 12-12-1999, 10:14 PM
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Re: Rough Idle

Two things you might check: The Idle Air Control valve and the EGR valve. The IAC valve is near where the two big rubber hoses meet the intake plenum chamber. You can remove it to see if it's gunked up. The EGR valve can be tested using a vacuum pump.


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post #5 of (permalink) Old 01-05-2000, 01:22 PM
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Re: Rough Idle

Well, after running my code scanner, It came up with 34 (EGR) and 42 (Exhaust Gas Oxygen sensor, voltage signal always rich does not switch. I replaced the EGR and the EGR valve position sensor and the O2 sensor. I'm still getting the 34 and 42 codes after replacing the parts. Any suggestions? If the IAC was bad wouldnt it show up on the code scanner? I'm getting tired of spending money and not getting results. The engine still runs the same okay until warm up then surging idle with a lot of hesitation.

post #6 of (permalink) Old 01-05-2000, 02:53 PM
 
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Re: Rough Idle

Kris: My 88 Bronco is doing the exact same thing and I changed the same parts (EGR Valve and O2 Sensor). I also removed the throttle body and cleaned it out along with the Idle Air Control Valve. My symptoms have improved, but I still have the idle surge. I was getting TERRIBLE gas mileage before the fix, too (6MPG). I haven't driven it enough to find out whether the milage has improved. Let me know if you figure out what's the cause of your problem! Good Luck!

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post #7 of (permalink) Old 01-05-2000, 05:52 PM
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Re: Rough Idle

My 88 302 EFI had a ruff start up and would even stall sometimes at stop lights. I checked everything and ended up grabbing a can of carb cleaner and spraying it around the butterflies. I could see a little build up on the walls. It cleared things up just like that. My idle was down to about 550. It jumped right back to 700 where it belongs and runs fine now. Be carefull of my advice though, I think I read on the list once that Ford recommended a special cleaner for this because of the sensors in there. haven't notice any adverse affects, but I have only done it once.

[img]/wwwthreads_images/icons/cool.gif[/img] MG48 - 88 Bronco
post #8 of (permalink) Old 01-05-2000, 07:54 PM
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Re: Rough Idle

I had the same code on my Bronco (#42 rich condition detected), mine turned out to be the fuel pressure regulator. It got so bad that my plugs were black as hell and there was gas in the oil....My previous posts about it are on Page 4.

post #9 of (permalink) Old 01-06-2000, 06:22 AM
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Re: Rough Idle

>>>Kris, did you clear the codes after you made the repairs? A mistake some people make is to not clear the codes. It will do it on its own after about 90 run cycles. Your code scanner can clear them or you should be able to do in manually by disconnecting the battery for a couple of minutes. This will erase the computers memory. The $30 dollar code scanners are not always accurate, since one sensor can make others malfunction, but, return to normal when the bad one is replaced. It may be worth it to take it to a shop and pay about 50-80 bucks to let their computer pin point it for you. Then you can replace the right piece. Hope this helps. Laters.

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post #10 of (permalink) Old 01-06-2000, 08:36 AM
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Re: Rough Idle

Like Mudmonger says, you could be getting led astray by a code still stored in the Keep Alive Memory.
If it were mine, here are a few things I would do:
Clean IAC and holes from IAC mounting into Throttle Body. You probably have a two-part IAC, so after you pull it off, you can pull two screws to separate the actual motor from the valve, then you can blast away with solvent without worry on croaking the motor.
Check EGR vacuum drive - With engine warmed up and running, pull off vac hose at EGR valve. Shouldn't be any vac on hose at idle. Run idle up to ~2500, should have vac on hose.
If you have a Fuel Pressure gauge, Key ON, Engine OFF pressure should be around 39 pounds, give or take. Leave it sit like that for a while. If it bleeds down fast, you could have a leaky injector, making it too rich, which would be a problem at warm idle. But leaking down without further troubleshooting doesn't have to be an injector. Could be fooled by bad fuel pump check valve, etc. More troubleshooting needed there if it goes down fast.
Start engine, fuel pressure should remain about the same (warning, pressure drop across the injectors should remain the same, but with engine running, the injector tip is now at vacuum, and fuel pressure reg. has vac line to sense intake vac, so operating pressure is what you read on the gauge, then add pounds of pressure negative below atmospheric.) So if you have 20" of intake vac, 20 divided by 30 inches of Mercury (atmos press.) = .666, then times 15 pounds (atmos press. in pounds) = 10 pounds, add that to what you read on the fuel pressure gauge when running. You're looking for far-off pressure values as bad, not just some off, as EEC will adjust injector duration using Oxy sensor, and tune out some variations.
That's were I would start, but it depends if you have the equipment.
Your problem doesn't have a clear solution, if those codes really are correct. Oxy too rich, and you already replaced the sensor, seems to say that the EEC can't get the mixture lean enough, no matter what it does on injector duration (it has a min. duration, will not go down to zero when running). That could point to too high fuel pressure (regulator, clogged/restricted fuel return line), but the EGR code is a joker there. EGR exhaust port in intake manifold may be plugged, killing EGR no matter what the valve does, or vac solenoid to EGR could be having problems, but that doesn't fit with the bad idle, as no EGR should be present then anyway. So some troubleshooting is definitely needed. Just some thoughts!
Sorry about my long posting, guys, but this is more complex stuff. Next weeks project - Troubleshooting the Mars Polar Lander, remotely, using only a test light :-)

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