Question about 1990 Ford Bronco II

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Erratic idle and loss of power

I have an 87 bronco ii, with a 2.9 liter engine. When I start it up in the morning it idles and dies and I have to give it gas to keep it going like a carburated engine that doesn't have a choke on it. In the afternoon (at times) it will start up and idle ok, but just like in the morning it has no power. I can floor the engine and barely get up to 50 mph. I have replaced the coolant temp sensor, map sensor, idle air solenoid, egr valve sensor, and throttle position sensor. I put in new plugs, distributor cap, rotor, and new wires. It has 219,000 miles on it. It has never used a drop of oil and still doesn't. Oh yes, when it does start idling on it's own the engine surges up and down constantly till it warms up, then it has high idle. The only thing I haven't replaced is the oxygen sensor. Someone told me there is an air temp sensor, but I can't find it. Please help. I am out of ideas.

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  • garywv54 Sep 07, 2008

    I bought a scan tool, but The only test connector I can find is the large one. There is supposed to be a single wire test connector to plug up to test tester along with the large one, but I cannot find it. I don't think it's a fuel pressure problem, because the erratic idle stops when the engine is warmed up.

  • garywv54 Sep 07, 2008

    I did check and replaced the air filter and there is no obstruction with the air intake sysstem

  • garywv54 Sep 07, 2008

    none of the web sites I looked at helped.

  • garywv54 Sep 08, 2008

    I disconnected the O2 sensor and it idled the same. Although the engine had only been off for 2 hours.

  • garywv54 Sep 09, 2008

    My 87 bronco II idles very rough on cold startups. It idles up and then dies. I have to keep giving it gas as you would a carburated engine without a choke. It's a 2.9 liter. I have replaced all sensors except the O2 sensor. When the engine warms up it will idle but surges up and down till it completely warms up and it will idle ok but it has no power when accelerating above 45.It does seem to idle fast when I stop. I did also change the air filter, plugs, wires, distributor cap, and rotor.

  • garywv54 Sep 11, 2008

    I have changed all sensors for my erratic idle problem. Today I changed the O2 sensor, so it's definitely not a sensor problem. I am leaning to either a distributer or a fuel problem.

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Dear sir From my own experience I suggest if you experience the problems listed above to get down your local scrap-yard and try the sensor that fits to the unit (its controls the idle apparently). If this fails, I'd try a 2nd hand AFM/TB to confirm that is at fault. The scrap-yards we did visit in Birmingham were happy for us to test their part and only to pay if it cured the problem - definitely worth trying to diagnose the problem, unless you fancy shelling out the best part of £300-500 bills on a remanufactured one only to find out it isn’t at fault. Hope you find this useful and it saves you time.
thanks............................please rate it

Posted on Sep 11, 2008

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Hello,
This problem is due to the temperature of the Engine,while you start in the morning you raise the accelerator for 1 or 2 mins it will be idle after getting some heat.This will happens many times.


Thank You

Posted on Sep 11, 2008

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Peace,
ngafm The fllet man for 20 years.


Sounds to me like a bad choke if its every single morning!
and or a vacuum leak that's worse in the morning when the engine is cold!
only other mechanical thing if it is intermittent would be a broken baffle in the cat converter the moves around and sometimes restricting exhausts from leaving!

ngafm, the fleet man!
When you find out its mechanic and not electronic then I deserve the best rating at this site!

Posted on Sep 09, 2008

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Hi,

If I may add.... pls try:

  • check for vacuum leaks. Spray ether or starting fuel on the junction of the intake manifold and the cylinder head, along the intake gasket when idling rough. If the idle changes, then gasket leak is confirmed;
  • additionally, pls check the vacuum hoses including the one leading to the hydrovac. You can also try temporarily removing the vacuum lines and plugging them so as to confirm leak in any of the hoses;
  • check compression.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards. Thank you for using FixYa.

Posted on Sep 09, 2008

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The quick test connector you need is attached to the same harness as the larger one, follow the harness down you will find it, your car is OBD 1, not OBD 2 as expert ginko said, the test connector is under the hood. Test the fuel pressure at idle, it should be around 35-40 PSI, also pull the vacuum hose off the the MAP sensor and blow through it, if you hear a gurgling nose replace the hose, it may be blocked with sealant gel from the MAP sensor, check the EGR valve for leakage, it should not be hot at idle, if it is it is leaking, clean the Idle Air-bypass Valve and the throttle valve, I am sure they are full of sludge, then clean the fuel injectors, this year of engine is prone to injector clogging, the fuel spray or-fices in the injectors are very tiny.

Posted on Sep 09, 2008

  • yadayada
    yadayada Sep 09, 2008

    Have you checked for an intake manifold leak? use a can of carb spray, spray all over the top of the engine and see if the idle speed changes, I really think you have a vacuum leak at the intake.

  • yadayada
    yadayada Sep 09, 2008

    By the way check the passenger side of the engine compartment for the self test connectors, they are there I assure you, some times they fall down onto the wheel well liner and are hard to see.

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It sounds like one of your cylinder may not be firing. check yor spark plugs. when it starts running - what is your exhaust like is there lots of water dripping from tail pipe. - you have no pressure regulation. Hope some help

Regards

Posted on Sep 07, 2008

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It can be the o2 sensor. I would recommend picking up the factory service manual so that you can check all of these with a multimeter and know if they are good or not.
Thanks,
Lee

Posted on Sep 07, 2008

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If you dis conect all our oxygen sensor start and try it if its the sensor our broncoe will run better it a easy test and cost nothing the computer will set the value of sensor at around .450mv try it out pierre

Posted on Sep 07, 2008

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Check the spark plugs, to ensure that it is not a distribution problem.

On fuelling check that fuel has enough pressure, and that air filter is ok and air intake is not obstructed.

If the problem is nor fixable with regular maintainance like the operations above, then you will need to connect a code reader to the car ECU (computer) , and start troubleshooting from the error ccodes that you get.

Posted on Sep 07, 2008

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