Question about 1998 Ford F250 SuperCab

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Engine missing rough idel and running at speed

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  • skip2469 Oct 14, 2008

    engine misses and runs rough from idel on up. also check engine light comes on steady and thens starts to flash just after hard acceleration. also exhaust port temps are about 100 to 150 deg f. on front two driverside cylinders ( I would refer to them by proper cyl # but I dont know the proper sequence on this block 2006 5.4 triton in f-250

  • Buddy762 Nov 28, 2008

    Where do I look to find the Spark Plug and Cylinders?

  • james legros May 11, 2010

    what year is the vehicle and what engine

  • Anonymous Mar 26, 2014

    engine misses at idle speed-not apparent when at running speed



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Check your coilpacks the 5.4 has a coil pack for each plug and they are known for going bad!

Posted on Oct 18, 2008

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Hi you need to find out what the fault codes say but if the two cylinders are next to each other and are running to hot the miss-fire is on these two cylinders do a compression test on these two i suspect the head gasket has gone between the two if everything is ok have a look at the distributor cap and rotor yates210456

Posted on Oct 14, 2008


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SOURCE: engine runs rough at certain speeds 3.0 v6 flex-fuel 1999 ranger

Check and see if the EGR valve is leaking, to check this spray water on it at idle, if the water steams off the valve is leaking and is the source of your problem, also are you sure you hooked the new DPFE sensor up right? re-check it..

Posted on Nov 23, 2008

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SOURCE: rough idel and no power on my 95 aspire changed

Check for leaking vaccum lines from the engine intake manifold. If no leak, test the IAC motor and clean out the air bypass passages per instructions below. Let me know if this doesn't solve the problem or you have any questions.

The Idle Air Control Bypass Air (IAC BPA) valve consists of an idle air control valve and a bypass air valve. The bypass air valve functions during cold engine conditions to increase engine idle speed. It consists of a thermowax bead and a valve.
Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation below 140°F (60°C), the thermowax is contracted enough to allow the valve to open. As the coolant heats, the thermowax begins to expand. When the coolant reaches temperatures above 140°F (60°C), the thermowax expands and closes the valve.
The valve controls the amount of throttle valve bypass, which ensures a smooth idle under all engine operating conditions.

  1. When the engine is cold, air flows through the valve during all modes of engine operation, to maintain the factory set idle speed.

TESTING See Figures 1, 2 and 3 (if you don't have an ohmmeter, skip this test)

  1. To check the Idle Air Control (IAC) valve resistance, unplug the IAC valve connector.
  2. Connect a high impedance Digital Volt Ohmmeter (DVOM) to the terminals.
  3. Measure the resistance.
  4. The resistance should be 7.7-9.3 ohms.
  5. If the resistance does not meet specification, replace the IAC BPA assembly.

Fig. Fig. 2: Connect an ohmmeter to the IAC valve; the resistance should be 7.7-9.3 ohms

At this point, if your IAC checks good, I recommend you take out the 4 screws seen above, remove the motor, and clean out the air passages/valve with carb cleaner. Also remove the big (3 inch diameter) hose from the throttle and clean out the throttle body, if dirty.

If the IAC tests bad, go to the removal and installation directions below.

The next test requires a scanner. If you don't have a scanner, skip this test.

  1. To check the BPA valve function, remove the BPA valve from the engine.
  2. Wait until the valve reaches room temperature. When the valve is cold, blow through the air inlet and verify that air flows freely through the valve.
  3. Heat the valve with a hair dryer; the air valve should move out and block the passage.
  4. If the valve does not function as specified, replace the IAC BPA assembly.
  5. To test the solenoid, connect a scan tool to the Data Link Connector (DLC).
  6. Turn the key ON and enter the simulation test.
  7. Access the IACV Parameter Identification (PID) and turn the dial to cycle at 75 degrees.
  8. Listen for the IAC solenoid to click when using the simulation test.
  9. If the solenoid clicks it is working properly.

Fig. Fig. 3: Idle Air Control Bypass Air (IAC BPA) valve assembly components


  1. Disconnect the negative battery cable.
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
  1. Drain the coolant until it is at a level below the Idle Air Control Bypass Air (IAC BPA) valve.
The lower coolant line should be disconnected after the valve is separated from the upper intake manifold.
  1. Tag and disconnect the upper coolant hose from the valve.
  2. Unplug the valves electrical connector, then loosen the two nuts and two bolts attaching the valve to the upper intake manifold.
  3. Pull the valve from the manifold and disconnect the lower coolant line from the valve.
  4. Remove the valve and gasket from the engine.
To install:
  1. Use a scraper to clean any old gasket material from the valve mounting surface.
  2. Install a new gasket and connect the lower coolant line to the valve.
  3. Install the valve and its retainers. Tighten the nuts and bolts to 71-88 inch lbs. (8-10 Nm).
  4. Engage the valves electrical connection and the coolant hoses to the valve.
  5. Fill the cooling system and connect the negative battery cable.

Posted on Dec 05, 2010

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