Rough Idle (Cold) 4.0 What next?
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Junior User
Joined: Nov 2003
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Rough Idle (Cold) 4.0 What next?
99 Ford Explorer, 4.0 engine. 99K miles.
Had code for "random multiple misfires". Replaced plugs with OEM, replaced plug wires, installed new coil pack. No more "check engine" light. No codes stored. A recent tune-up included new fuel filter, air cleaner, and PCV valve.
What next? It still idles really rough for a couple minutes at start-up, then smooths out and runs perfectly. Re-starts with hot engine are smooth. Only complaint is the really rough idle for a couple minutes at cold start-up.
I've searched high and low for vacuum leaks or loose connections and found nothing.
Any thoughts? Stuck EGR valve? Something I'm missing?
Had code for "random multiple misfires". Replaced plugs with OEM, replaced plug wires, installed new coil pack. No more "check engine" light. No codes stored. A recent tune-up included new fuel filter, air cleaner, and PCV valve.
What next? It still idles really rough for a couple minutes at start-up, then smooths out and runs perfectly. Re-starts with hot engine are smooth. Only complaint is the really rough idle for a couple minutes at cold start-up.
I've searched high and low for vacuum leaks or loose connections and found nothing.
Any thoughts? Stuck EGR valve? Something I'm missing?
Post Fiend
Joined: Jan 2003
Posts: 9,748
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From: Connecticut
Could be a lower intake gasket leak issue. The symptoms you describe are a few of the classic indicaters of a gasket problem. Coolant could be getting into cylinders from the coolant ports, causing cold misfires and a stumbling idle.
I recommend having a used oil analysis (UOA) performed next tiime you change your oil. It's how I helped to confirm my own Ranger 4.0L intake gasket problem. The coolant also leaks into the oil, so the sodium and potassium will show up in the UOA. You should keep in mind that coolant kills bearings.
Blackstone Labs will send you a free sample kit that makes it easy to send them an oil sample: http://www.blackstone-labs.com. Around 20 bucks.
I recommend having a used oil analysis (UOA) performed next tiime you change your oil. It's how I helped to confirm my own Ranger 4.0L intake gasket problem. The coolant also leaks into the oil, so the sodium and potassium will show up in the UOA. You should keep in mind that coolant kills bearings.
Blackstone Labs will send you a free sample kit that makes it easy to send them an oil sample: http://www.blackstone-labs.com. Around 20 bucks.
New User
Joined: Jun 2004
Posts: 5
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From: Florida
I had this problem for a while. My Ranger wouldn't idle when it was cold, or when it had been raining. Once it warmed up, it would idle fine. Finally, it quit idling good all together, and I had to drive around and keep my foot on the gas at red lights to keep it running. The idle air control valve went bad. Put a new one on, and it ran perfect. . might want to look in to that.
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Still Idles Rough When Cold
My wife's Explorer still idles rough when cold. 
She has the OHV engine. The IAC was replaced about 5K miles ago when it went bad.
When she starts it in the morning it still idles rough for about 4-5 minutes, then smooths out, and runs perfectly the rest of the day.
Pulling out what hair I have left!
She has the OHV engine. The IAC was replaced about 5K miles ago when it went bad.
When she starts it in the morning it still idles rough for about 4-5 minutes, then smooths out, and runs perfectly the rest of the day.
Pulling out what hair I have left!
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Junior User
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Code P0303 Is Back
I checked the #4 and #5 plugs and no fouling was noted.
The "check engine" light came back on today!
Code P0303 was stored. Misfire plug #3. Guess I need to look at that plug too?
The "check engine" light came back on today!
Code P0303 was stored. Misfire plug #3. Guess I need to look at that plug too?
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