Idles very rough when cold
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Idles very rough when cold
My 1994 F150 V8 starts up strong every time. Runs strong for about 2 minutes, then idles very rough and will stall if I don't keep it running. I keep it going for 5 to 7 minutes then it seems to kick in and run great. If I try to drive it cold, it bogs out then kicks in, then bogs out then kicks in... until warm. It will idle rough once in a while after it's warm, but mostly runs great. The garages have not looked into it, but each one said run it for a few weeks, it may come out of it. That was 4 weeks ago. None had any specific ideas. This is the process EVERYTIME it starts cold. Any ideas???
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Check for stored codes in the engine computer before spending a dime on any parts. Warm the engine up then follow the instructions here to "pull the codes" and run the Key On Engine Off (KOEO) test: How To Run a Self-Test
Fleet Owner
Joined: Oct 2005
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From: Kentucky
See my previous reply. Before spending another dime on parts find out for yourself what the PCM (computer) thinks is wrong. Then you can go from there. The link I gave you also has links on the right side of the page to decode any codes you may find. Your '94 will display 3 digit codes.
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Mindy just for info. when first cranked the computer doesnt use the O2 sensor. The sensor has to heat up to about 600 to 800 degress F before it will give a signal. The computer fires the injectors with a pre programed or fixed signal for a few minutes and then swaps to the O2 sensor. If the sensor is bad , the computer will try to use it for a while to be sure it is bad then give the check engine light or error code. It will then revert back to the pre programmed signal to the injectors.
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Thank you. I am not mechanical, but did research my "having to warm it up" problem. I did read that about the 02 sensor, so I could not really make sense of it having to warm up before it would run, But the 02 sensor seemed to be the place to start. The 02 sensor is the only thing I had changed, they did say it was broken. It runs great when cold now. Doesn't skip a beat. Thank you for the info.
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Mindy, go here for a little lite reading on an O2 sensor OXYGEN SENSORS . or here AA1Car Auto Diagnosis & Repair Articles for other articles on how cars work. here is another good info place WELLS Engine Management Systems - Counter Point Newsletter
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