1989 Ford Bronco rough idle

Tiny
MIKEM367
  • MEMBER
  • 1989 FORD BRONCO
  • V8
  • 4WD
  • AUTOMATIC
  • 25,000 MILES
My 1989 ford bronco w/351 / 25000 on rebuilt engine and auto trans has a rough idle. I got it used and the owner said it has 25000 on this rebuilt engine but I don't know for sure. I took it straight to a garage and they replaced the O2 sensor and the TPS. They told me they had to adjust the timing higher than normal to get it to idle better. I also own a 1990 bronco w/302 and when I compare the two distributors, the '89 is sitting much farthur to the left. I am thinking that the distibutor could be one tooth off. It idles at 900-925 rpm and always feels rough, like it may cut off at any time. On the open road it runs great. Also with the idle set so high, it makes the engine hard to start when it's hot. Any clues?
Sunday, May 10th, 2009 AT 6:11 PM

9 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Try cleaning out the idle air control valve/motor and see what happens
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Sunday, May 10th, 2009 AT 6:54 PM
Tiny
MIKEM367
  • MEMBER
  • 10 POSTS
Thanks, but sorry that doesn't work. I tried switching the one from the '90 bronco onto it and it didn't change. It doesn't knock off but it sure feels like it's going to at any minute.
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Monday, May 11th, 2009 AT 3:22 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
If you cleaned the IACV passages and you have tried with another-check below components

Check the fuel pressure/vacuum leaks/PCV and EGR valves for leakage

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
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Monday, May 11th, 2009 AT 6:20 PM
Tiny
MIKEM367
  • MEMBER
  • 10 POSTS
Well I tried all that and I give up. I'll take it to a professional garage and probably pay more than the truck is worth. Thanks.
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Thursday, May 14th, 2009 AT 5:58 PM
Tiny
MIKEM367
  • MEMBER
  • 10 POSTS
I want to buy a code scanner to use on my 1989 and '90 broncos. I have been shopping around and I've noticed that a lot of the products say they are for 1996 and newer cars. What brand of scanner can I get that will work on my older broncos.
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Monday, May 25th, 2009 AT 9:35 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You can get the code reader from us click on my signature block link for TOOLS>

Actron CP9015 Ford Code Scanner
Actron CP9015 Ford Code Scanner Compatible with OBD I 1981 - 1995 Ford & Lincoln-Mercury (PDF) vehicles Retrieves engine trouble codes from the.
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Monday, May 25th, 2009 AT 3:35 PM
Tiny
MIKEM367
  • MEMBER
  • 10 POSTS
1990 ford bronco w/5.0. I just removed the top of the engine to repair an oil leak coming from the back of the lower intake manifold. Engine ran great before. I replaced the intake gasket, (upper and lower), changed all eight fuel injectors, and a new egr valve and position sensor. The engine cranks great but won't even try to start. I've checked for spark at one of the plugs and i've got that. The distributor is definitely back in the same place as before and I can smell the fuel around the engine so it should be getting fuel. The fuel pump comes on so I know it works. It ran great before I started this project, now I got nothing. Any ideas?
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Saturday, June 6th, 2009 AT 6:12 PM
Tiny
RASMATAZ
  • MECHANIC
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The fuel pump comes on so I know it works

You need to actually check the fuel pressure with a fuel pressure gauge. The fuel pressure with engine running should be 30-45psi
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Sunday, June 7th, 2009 AT 10:13 AM
Tiny
89BRONCO4X4
  • MEMBER
  • 3 POSTS
Where is the plug for a code scanner for a 89 bronco full size
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Monday, August 8th, 2011 AT 2:28 AM

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