R50 Automatic transmission - problems with changing gears, engine revving

[dareno]

Hi, recently I am experiencing strange problems. It looks like automatic transmission can't shift the gear and engine is revving. When I release the pedal for a moment and press it again then the gear is shifted.

Look at the video:


I am going to go to a shop to fix it. But first I would like to know what kind of defect is this in order not to get cheated easily.
Is there something I could check myself?

The oil looks clean, bright pink. Whenever I check oil level on engine running and warm the stick always is wet about HOT sign. Transmission oil was replaced in November 2012 at about 108 k miles, now it is about 124 k miles.

[lrwhat]

Throttle position sensor would be 1st to replace best of luck

[atraudes]

Ooo, good call. Check the FSM; it has some diagnostics you can run on the TPS before you get a new one. It also has the calibration steps if/when you replace it.

The good news is that's a healthy sounding engine!

[attofarad]

What year is your Pathfinder? For 2001, there was a TSB for something similar, but mine (and my coworker's) was not as high-revving radical as yours. Based on that, I doubt that it is your problem, but here is what happened to mine and others:

- when starting up in cool, but not really cold weather (maybe 10C /50F), the transmission would slip/engine rev when going from 1st-2nd or 2nd-3rd. If I understand correctly, the system was over-compensating for cooler temperature, where it would reduce pressure to make shifting less harsh with cooler/thicker fluid. Once warmed up, or even if starting really cold and getting on the highway before it warmed up, never a problem. The fix was twofold: 1) replace the transmission control unit (under dashboard at far left/kick panel) and 2) replace the solenoid pack inside the transmission. I replaced my wife's 2001 QX4 control module with one out of a 2002 wreck (~$65 from eBay), which seemed to fix the 1st-2nd issue, and maybe improved the 2nd-3rd slightly. I told her I'd replace the solenoid pack if she paid for it ($300 or so), but she decided to let it slip once in a while. My coworker never did anything with his, and sold it with 265k miles on it.

[dareno]

Thank you guys for your input here. The Pathfinder is 2003 year.
I would like to check TPS as I just read about it and symptoms are similar.
I have a question: can I just unplug TPS and drive to check like guy in this video:
https://www.youtube.com/watch?v=cPkk6md3Sy0

Is TPS the one near green circle on this picture?


UPDATE:
Current symptoms are such that I can drive up to 40 km/h and then engine is revving no matter if I drive fast or slow.

[Buzzman]

What you have circled is the Idle Air Control Valve (IACV).
The Throttle Position Sensor is at the end of the throttle shaft.
It has the two plugs, the brown and the grey one, to the right of the throttle body opening.