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Old August 22nd, 2010, 05:45 PM   #1
big_ol_bronco78
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Default 91 explorer runs rough cold

I have a 91 explorer with the 4.0, it seems to idle and run rough, has little miss fire, when cold, but after driving a few min, like 5 min, runs fine. Anyone know what this could be, previous owner did plugs and wires and put on new water temp sensor. thank
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Old August 22nd, 2010, 07:15 PM   #2
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I had the same issue on a 92 ranger with the 4.0 and it was the air bypass valve on the intake. It wasnt opening all the way when cold, but just enough to not throw a trouble code or light. I have had luck with cleaning them a little and reinstalling just make sure you use a new gasket and not silicone as it can do more damage than help. Just my opinion. Dan
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Old August 22nd, 2010, 07:42 PM   #3
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i'll give that a shot. thanks
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Old August 23rd, 2010, 09:03 PM   #4
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update, cleaned that out, made it idle better, see how it drives tommorrow
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Old September 8th, 2010, 06:45 PM   #5
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agreed on the IAC valve... made mine idle high this winter... perhaps the MAF too... those are the two i always checked when the 4.0 ran like crap
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Old September 8th, 2010, 10:43 PM   #6
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I agree with these guys. Did it to the 96. Both the MAF and the IAC. Just make sure to let them dry well.
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Old September 9th, 2010, 04:20 AM   #7
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carbon in the IAC is a common problem, and cleaning normally solves it. They rarely fail. I consider cleaning that and the throttle body/intake, etc part of a tune up. I have also pulled MANY of them, cleaned them, and put them back on with the same gasket, with no issues at all.

Ford used to make a cleaner that worked extremely well (D9AZ 19579 AA...wow, I still remember the part number after about 10 years...wtf?) but they want to sell parts, so now they make a sticker that says not to clean in side these parts
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