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I have a 2000 3.3 V6 4x4. As the title suggests, the engine was operating fine (just leaking oil) until I replaced both valve cover gaskets which requires removal of the upper plenum, along with several coolant/vacuum/air hoses. I made sure all electrical connections physically and audibly clicked back into place along with properly torquing the plenum bolts. I didn't replace any vacuum hoses as they all came off with minimal effort and visually looked good, unlike all the coolant hoses I destroyed getting off and replaced.

The vehicle now idles at 1800-2000+rpm upon startup. This is much higher than before and lasts much longer. It used to kick down immediately upon being driven. Now it stays at this higher idle until the engine is pretty much up to temp but still idles around 1100-1200 range once warm. I have a feeling something is wrong with the idle position sensor which I believe is bolted to the drivers side back and bottom of the plenum. Which means removing the plenum again to access the sensor area. Also, these symptoms seemed to get worse once the cold weather hit. I'm hoping someone more knowledgeable than myself about these symptoms might offer other suggestions before I take this all back apart again, ugh.

All that being said, the good news is my valve cover gaskets are no longer leaking lol. Love fixing one thing just to cause another issue!
 

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Before resorting to yanking the upper plenum again, I'd probably break out a can of WD-40 and start spraying it around to look for vacuum leaks.

Notice a sudden change in idle speed when you spray a particular spot, and you've found your leak.
 

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I have a 2000 3.3 V6 4x4. As the title suggests, the engine was operating fine (just leaking oil) until I replaced both valve cover gaskets which requires removal of the upper plenum, along with several coolant/vacuum/air hoses. I made sure all electrical connections physically and audibly clicked back into place along with properly torquing the plenum bolts. I didn't replace any vacuum hoses as they all came off with minimal effort and visually looked good, unlike all the coolant hoses I destroyed getting off and replaced.

The vehicle now idles at 1800-2000+rpm upon startup. This is much higher than before and lasts much longer. It used to kick down immediately upon being driven. Now it stays at this higher idle until the engine is pretty much up to temp but still idles around 1100-1200 range once warm. I have a feeling something is wrong with the idle position sensor which I believe is bolted to the drivers side back and bottom of the plenum. Which means removing the plenum again to access the sensor area. Also, these symptoms seemed to get worse once the cold weather hit. I'm hoping someone more knowledgeable than myself about these symptoms might offer other suggestions before I take this all back apart again, ugh.

All that being said, the good news is my valve cover gaskets are no longer leaking lol. Love fixing one thing just to cause another issue!
Did you ever figure this out? I'm having the same issue after I replaced my intake gaskets upper and lower.
 

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Did you ever figure this out? I'm having the same issue after I replaced my intake gaskets upper and lower.
Same here. Just finished replacing the plugs and fuel injectors and various hoses and vacuum lines on my 2001 Frontier, 3.3 liter crew cab XE and the idle won't drop even after warming up. It's running great compared to how it was doing prior to the service, except for the idle.
 

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It takes time for the ECU to "relearn" to the new idle point. There is a "relearn" protocol but it did not work in my 4.0L What worked was time. The proper idle speed is 600-650 rpm. But my post engine surgery truck stayed at 750-850 rpm for weeks. In due time, the engine speed meandered down to the correct range.
 

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It takes time for the ECU to "relearn" to the new idle point. There is a "relearn" protocol but it did not work in my 4.0L What worked was time. The proper idle speed is 600-650 rpm. But my post engine surgery truck stayed at 750-850 rpm for weeks. In due time, the engine speed meandered down to the correct range.
Thank you. It settled down pretty quickly for me after driving several miles. It was one of those "what did I do wrong?" moments when I started it up and it ran like crap. Slight panic.
 
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