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Discussion Starter #1
I recently got a high-mileage pathfinder with a very leaky valve cover and a "transmission problem". Fixed the leak, changed plugs, put everything together. It runs very well at low throttle, shifts very smoothly, up to the 70MPH max I've tried so far. Give it more throttle ( at speeds between 35 and 55) and it starts to buck. Does not shift but loses speed, returns to the speed it was, and cycles this way within a 2-second cycle. This happens at around 2800RPM. Increasing throttle makes no difference but backing off returns it to smooth running and one can gently sneak it to higher speeds.

If the power valve is causing this what's the fix? Since the car is pretty powerful, could I just remove the vacuum actuator for the power valve and go on my (slower) way? Would the PCM gods be upset if I did that?

Thanks in advance for your thoughts, guys!

John
 

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Discussion Starter #3
I recently got a high-mileage pathfinder with a very leaky valve cover and a "transmission problem". Fixed the leak, changed plugs, put everything together. It runs very well at low throttle, shifts very smoothly, up to the 70MPH max I've tried so far. Give it more throttle ( at speeds between 35 and 55) and it starts to buck. Does not shift but loses speed, returns to the speed it was, and cycles this way within a 2-second cycle. This happens at around 2800RPM. Increasing throttle makes no difference but backing off returns it to smooth running and one can gently sneak it to higher speeds.

If the power valve is causing this what's the fix? Since the car is pretty powerful, could I just remove the vacuum actuator for the power valve and go on my (slower) way? Would the PCM gods be upset if I did that?

Thanks in advance for your thoughts, guys!

John
Sorry, I was trying to determine what they call the (vacuum-operated ?) set of 6 throttle plates which sit in the lower plenum. My car is a 2004 3.5L DOHC v6 Pathfinder. The transmission is automatic and I think it's a RE4R01A.

Thank you so much
 

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They are called "swirl control valves". They are normally closed at idle/low RPM, then gradually start opening as the RPMs increase. One of the first things to do is perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores or online at Amazon.com. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction. If you have a copy of the FSM for your vehicle, the code readout procedure is described there along with a listing of codes. You can download a copy of the FSM from these web sites: Nissan Service Repair Manuals or Owner's Manuals. The section EC.PDF is the one you need to read.

From your description of the symptoms, it sounds like maybe there's a problem with the MAF causing the ECU to put the system into"fail safe" mode which limits the RPM to around 2,000 RPM or so. It's also possible that the fuel pressure is not to spec.
 
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