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MikeB85, ASE Certified Technician
Category: Ford
Satisfied Customers: 354
Experience:  ASE Certified, I-Car Trained and Certified, Automotive Technology Degree
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1992 Ford F-150: Idles rough then smooth then rough

Customer Question

1992 Ford F-150 4.9 standard. Idles rough then smooth then rough. No power. At times will pick up and go then back to rough. What is causing this problem
Submitted: 8 years ago.
Category: Ford
Expert:  MikeB85 replied 8 years ago.

Your vehicle is equipped with an idle control system that is controlled through the ecm. If there is a fault in the system it should throw a trouble code. It is possible that you have an issue with the Idle Speed Control solenoid. You can test the solenoid using a digital multimeter that can measure resistance. Disconnect the the harness connector from the solenoid. Set the multimeter to the 200-Ohm scale. Now measure the resistance between the connector terminals. (I have a picture below to help you out.) There is a diode in the solenoid. Connect the multimeter positive test lead to the VPWR terminal and the multimeter negative lead to the ISC terminal. The resistance should be 7-13 ohms. If the resistance doesn't fall in this range then replace the Idle Speed Control Solenoid. I priced this item on Auto Zones website and it lists for around $50. Let me know if you have any other questions. Thanks.


Customer: replied 8 years ago.
Reply to MikeB85's Post: I'm asking for my next door neighbor. (no computer. living in the dark ages) Will check with him in AM. Thank you
Expert:  MikeB85 replied 8 years ago.
Not a problem. Let me know what he comes up with. Thanks.
Customer: replied 8 years ago.
Hi Mike neighbor states he's replaced EGR valve, Idle position, throttle sensor, plugs/wiring, rotator, distributer cap and control module.
He says its like no fuel or fire. Then picks up and runs then drops down. Misses. No power.
He asks could it be clogged catalytic converter? That is his inclination.
Expert:  MikeB85 replied 8 years ago.
You can try checking the catalytic converter by hitting or shaking it to listen for any loose parts that may cause it to clog up and restrict the exhaust flow. This will cause loss of power and driveability problems. Although I still believe it could be an issue with the idle system. I would still do the test that I have listed above just to double check. This could also be caused by a possible short or open in the circuit for the idle speed control solenoid. This is what he replaced? Let me know if you have any questions.