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Old 07-18-2013, 02:12   #1 (permalink)
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Rough Start

I'm new to this forum. Looking for some help. When I leave my 1991 Bronco 5.0 302 sit for a couple hours and then go to start it starts up but immediately drops to about 200 rpm sounds like it is going to stall out and then after about 1 minute it idles normal. What are everyone's thoughts on what this could be. Just recently put new plugs and wires on and changed the fuel and air filter and hasn't made a difference.
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Old 07-18-2013, 02:28   #2 (permalink)
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Re: Rough Start

Could try replacing the engine coolant temp sensor for the PCM which lets it know how much fuel needed I.e more fuel on cold start .
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Old 07-18-2013, 02:36   #3 (permalink)
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Re: Rough Start

What is a PCM?
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Old 07-18-2013, 02:44   #4 (permalink)
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Re: Rough Start

Power control module .
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Old 07-18-2013, 04:17   #5 (permalink)
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Re: Rough Start

If your engine idles rough or stalls, your Ford Bronco might have a bad Manifold Air Pressure Sensor. You will have to test the MAP sensor. Follow the below steps to test the MAP sensor.

1) Locate the MAP sensor and disconnect the wiring harness from the MAP sensor. Each end of the sensor has a small tap. Pry the harness off the tap and pull the harness free of the MAP sensor.

2) Place a jumper wire between the terminals on the wiring harness and the terminals on the MAP sensor. Make sure the jumpers are bare wire and that they do not touch each other or any other metal component on the Bronco.

3) Turn the Bronco's key to the "On" position but do not start the engine. Place the leads of your multimeter onto the bare jumper wires and take a voltage reading. The voltage should reflect between 4.5 to 5.0 volts.

4) Start the engine and let it warm up to normal operating temperature. Test the voltage again. The voltage reading should be different. Have an assistant rev the engine several times. The voltage reading should fluctuate with the revving of the engine. If it does not, the MAP sensor is defective.
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Old 07-18-2013, 07:53   #6 (permalink)
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Re: Rough Start

^ Good shout re MAP sensor .
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