Rough idle
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Senior User
Joined: May 2001
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Rough idle
I have a '92 Bronco (5.0) that idles extremely rough regardless of engine temperature and gear selection. Check engine light appeared; changed o2 sensor and light went out. The engine at speed runs very well. I did clean throttle body and checked for vacuum leaks(didn't find any yet) Could air-bypass servo be dirty or failing? Throttle position sensor failing? Any assistance would be appreciated.
Elder User
Joined: Oct 2001
Posts: 974
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Rough idle
My first thought would be spark plugs, wires and fuel. I would check the plugs, run some fuel-injection cleaner through, and go from there. Chevron Techron works very well, but costs a little more. When I bought my '88 F-150, it ran rough. I found a short in a plug wire. Put on new ones, all good. Could also need a new distributor cap and rotor.
There are a lot of other factors, but it's good to start with the basics.
There are a lot of other factors, but it's good to start with the basics.
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Rough idle
Ok, I posted a similar question about three days ago and have gotten no response. My '92 5.0 is doing the same type of thing. If I read the post correctly, the rough idle is the only problem. As soon as the accellerator is touched things smooth out. I have changed all the obvious things like plugs, wires, cap, rotor, etc.. Even the fuel filter thinking low pressure may be the problem. Maybe we haven't got the same problem but it sounds like it. Does yours seem to get worse as the engine gets reaches operating temp.? My 5.0 is only a year old. I will be happy to post any info that I get in the meantime. Here's hoping somebody knows whats up.
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Senior User
Joined: May 2001
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Rough idle
These problems have to be the most frustrating. I too have eliminated simple things (tune-up parts) and had the egr replaced. My truck does seem to run worse at temperatures. I am going to continue to look for vacuum leaks (brake booster even). I wonder if the processors ever fail?
Senior User
Joined: Jun 2002
Posts: 241
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From: Colorado Springs, CO
Rough idle
I agree. I've done alot of work trying to find the problem and i still have a low idle speed and surging while stopped(sometimes).
How do you check for vacuum leaks? There are probably several spots, but I don't know where to check.
Brian
1988 Eddie Bauer 351 EFI
How do you check for vacuum leaks? There are probably several spots, but I don't know where to check.
Brian
1988 Eddie Bauer 351 EFI
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New User
Joined: Jul 2002
Posts: 14
Likes: 0
From: texas
Rough idle
i have 1986 302 eng has about 30,000 miles on it. it does the same thing i have changed cap,rotor,plugs,wires,fuel fliter inline fuel pump,egr valve and sensor,dist and module,tps sensor,map sensor,iat sensor,cleaned fuel inj,changed fuel reg.and even eec all no help.no codes on ecc but truck runs rich my guess is its a fuel inj, dripping.also change idle speed valve no help.going to try fuel inj next or live with it
does anybodys idle get better with a/c on .
does anybodys idle get better with a/c on .
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Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Rough idle
[updated:LAST EDITED ON 30-Oct-02 AT 02:38 PM (EST)]Mike 0454, sounds like you have taken a lot of time trying to work this kind of problem out and have replaced more than the rest of us in the process. If replacing injectors helps please let us know. I am willing to do that if it becomes necessary. I just don't want to spend that kind of $$$ for nothing.
By the way, since this problem just started in my '92 and its been chilly here, I hadn't realized 'til I used the defroster yesterday that the curb idle does seem to improve with the compressor running.
By the way, since this problem just started in my '92 and its been chilly here, I hadn't realized 'til I used the defroster yesterday that the curb idle does seem to improve with the compressor running.
Senior User
Joined: Jun 2002
Posts: 241
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From: Colorado Springs, CO
Rough idle
I think mine would work fine if I could increase the idle speed a little. If hovers at 600 when it has problems with surging. Anyone know how to do this on a fuel injected vehicle? What's a curb idle?
Brian
1988 351 EFI
Brian
1988 351 EFI
Hotshot
Joined: Oct 2002
Posts: 18,488
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From: The Big, Oregon
Rough idle
Has anyone adjusted the idle on your truck? If so, smack them, and reset it. I chased this problem around on an Explorer, and found that someone tried to up the idle speed with the screw on the linkage. Fords don't like this. Try taking off the IAS and cleaning or replacing it, and do the same for the egr. If these don't work, try closing down the throttle a little, about 1/2 turn on the screw. I know this sounds like reverse logic, but it should work.
Jared
Jared
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Rough idle
Curb idle is, running but not in gear. Hence in-gear idle is..well.
There is an idle adjustment on fuel injected vehicles on the throttle body but as was already posted, attempting to change this is a very bad idea. That adjustment is factory set to meet the needs of the engies, computer, and other sensors in the truck. If this changes, it rearranges way too many varialbes for the computer and such to accamodate without causing some sort of malufunction either immediately or shortly down the road.
There is an idle adjustment on fuel injected vehicles on the throttle body but as was already posted, attempting to change this is a very bad idea. That adjustment is factory set to meet the needs of the engies, computer, and other sensors in the truck. If this changes, it rearranges way too many varialbes for the computer and such to accamodate without causing some sort of malufunction either immediately or shortly down the road.
New User
Joined: Jul 2002
Posts: 14
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From: texas
Rough idle
sorry its a mitchell repair tsb,for rough idle
1985-87 5.o auto trans disconnect idle bypass solenoid connector.start eng. and run at 1800rpm for 30 sec. place trans in drive and check rpm should be 550rpm trun screw to get 550 rpm.shut car off and disconnect battery for 5 mins reconnect idle solenoid.start eng and idle for 2min then goose eng and let return to idle then if you made adjustment check tv cable adjustment.its a little differnet for later year if anybody wants it just ask i will post it
mike
1985-87 5.o auto trans disconnect idle bypass solenoid connector.start eng. and run at 1800rpm for 30 sec. place trans in drive and check rpm should be 550rpm trun screw to get 550 rpm.shut car off and disconnect battery for 5 mins reconnect idle solenoid.start eng and idle for 2min then goose eng and let return to idle then if you made adjustment check tv cable adjustment.its a little differnet for later year if anybody wants it just ask i will post it
mike