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86 2.9L idling rough/small surging/high idle


86RangerXL

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My 86 ranger with the 2.9 has been idling weird ever since I got it. Sometimes when I first start it up, it surges slightly, but goes away after I rev it for a second and doesn't happen when its warmed up. The bigger issue is the rough idle. It idles rough whether its warmed up or not, but seems to smooth out while driving. You can feel the whole truck shaking a little bit on random intervals while idling and can kinda hear it too. It idles really high to, to the point where it jumps a bit when I put it in gear.

I've heard that so many different things can cause idle problems and I can't just go throwing tons of parts at it, so I don't know what is causing this.
 


franklin2

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I threw tons of parts at mine, and it always did it. It was a 86 2.9 also. Ran great except at idle. I finally figured out it was idling a little rich. No codes, and tried everything. The only thing I didn't try was the fuel injectors. This truck had sit around some before I got it, so maybe the injectors are sticking. I didn't realize the injectors could have a problem like that till I see on here several guys had problems and it ended up being bad injectors.

You should do all the normal things first though;

1. Clean the throttle body
2. Clean the idle air control valve
3. Temporarily block the EGR to make sure it's not leaking
4. Check for any other vacuum leaks.
 

86RangerXL

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I threw tons of parts at mine, and it always did it. It was a 86 2.9 also. Ran great except at idle. I finally figured out it was idling a little rich. No codes, and tried everything. The only thing I didn't try was the fuel injectors. This truck had sit around some before I got it, so maybe the injectors are sticking. I didn't realize the injectors could have a problem like that till I see on here several guys had problems and it ended up being bad injectors.

You should do all the normal things first though;

1. Clean the throttle body
2. Clean the idle air control valve
3. Temporarily block the EGR to make sure it's not leaking
4. Check for any other vacuum leaks.
I cleaned the throttle body just a few weeks ago, the IAC is new, the EGR stuff is brand new, there may be a vacuum leak, but I can't seem to find any. I just tested the fuel injectors by ear and I can hear them all clicking consistently like they should except for cyl. 6 which I can't get to easily so I couldn't test it just by sound. Some people say the O2 sensor, the map sensor, or the TPS could cause it.
 
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franklin2

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A long time ago I had a SVO mustang and I took the injectors out and went to the Ford dealer and had them test them. He did right there when I was in the shop, they had a tester machine. It tested flow rate and he also said they check for proper spray pattern. If the spray pattern is not right or they shut off with a little dribble of gas, I think that could cause a rough rich idle.

That's the only thing I could come up with on mine. I was going to take them out and see if I could make my own tester with a old fuel pump but I never got around to it and it's not on the road now.
 

JerrySab

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Not to pee on your wheaties, but I think these old critters have a pretty lousy idle even when they're in great shape.

THAT SAID. New injectors will definitely help if they've never been changed. I was recently struggling with the exact same symptoms. I was stumped so I threw in the towel and finally took it to a mechanic. They attached an oscilloscope to various parts and found:
- TPS would randomly send DRIVE (like, full 5v) signal to PCM when truck is just sitting there. idle would spike. and remain until TPS stopped malfunctioning.

..also,
- Diesel stop screw on throttle body dialed in too far. RonD frequently gives the advice to only have the diesel stop screw dialed in enough to keep the throttle plate from sticking in the bore. He's right.

- small vac leak at throttle body. Easy gasket swap.
 

franklin2

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Did you ever figure it out?
In my case I blew up the 2.8 I had, so I took the troublesome 2.9 I had in the old truck in the backyard and stuck it in. Bunch of wiring and had to redo the fuel system since it is fuel injected.

Got it running and it ran terrible even worse than before. I then figured out the pin 30 was grounded any time you are in neutral or the clutch is pushed in. I hadn't wired that up. I just took the pin 30 wire and jumped it to signal ground. Truck straightened right out and that engine has never ran better. I just leave it jumped all the time.
 

rusty ol ranger

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Did you ever figure it out?
Every 2.9 (hell, every early EEC IV ford) ive owned has had a bit of a bouncy idle. Ive come to accept it as just the nature of them.

His high idle was more then likely a vacuum leak somewhere. Either a hose or bad intake gasket, bad TB gasket, etc. Rough idle at higher then normal RPM is classic symptoms of a vacuum leak.
 

newnthused

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Every 2.9 (hell, every early EEC IV ford) ive owned has had a bit of a bouncy idle. Ive come to accept it as just the nature of them.

His high idle was more then likely a vacuum leak somewhere. Either a hose or bad intake gasket, bad TB gasket, etc. Rough idle at higher then normal RPM is classic symptoms of a vacuum leak.
Okay thank you. But I can't find a solid answer from anyone about how to go about checking for a vacuum leak? Can you help me on where/how to look for such a thing. I know you said intake gasket. How would I check for that and is that a severe thing to change?
 

rusty ol ranger

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Okay thank you. But I can't find a solid answer from anyone about how to go about checking for a vacuum leak? Can you help me on where/how to look for such a thing. I know you said intake gasket. How would I check for that and is that a severe thing to change?
Best way (without a smoker) is to start the truck and spray carb cleaner around where the upper intake bolts to the lower and where the lower bolts to the heads...and listen for RPM changes. If the RPM doesnt change, then no leak, it does change, found your issue.

The upper intake gasket isnt bad, the lower requires removal of alot more shit.

If you want start a new thread describing your issue...youll get more/better answers
 

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