High or pulsating idle after driving on highway P11 g20

[mneleventhirty]

I bought a 2001 Infiniti G20t, last month. It is an automatic and had 129k miles and the SES light due to the rear O2 sensor (P0141), non-functioning AC and some rust near the wheel wells, but the interior was great and the body was straight, so could not refuse the asking price of $2500 for a trusty DD. AC worked after a recharge and I don't care about the rear O2, more trouble extracting it from the rusty innards. Had the valve cover gasket and the distributor O-ring seal replaced due to an oil leak, driver CV boot was torn, so had that replaced. Also noticed the PS high pressure hose leaking and the PS boot torn on the passenger side. So had the rack replaced with a good used one and the PS hose had to be sourced from dealer ($270 ouch!). The $2500 I paid initially is not looking cheap now.
But after doing the PS I notice that the idle sticks in high rpm- 1500 to 2000 in Park or Neutral, only after long highway drives at 60-70 mph. Also sometimes the idle goes up and down between 1500 and 2000 on it's own, as if I am revving it. It goes back to normal after a restart. Took it back to the shop to have it checked, to see if they messed up some vacuum hose or connector when replacing the PS and nothing came up. Did another scan and now I see code P0325 for the Knock sensor. But the issue I am seeing doesn't seem to be related to the Knock Sensor or so I think. The shop thought it might be IACV or TPS related, but I don't want to throw more money at it, if I don't have to, wondering if it is something more simple. This is driving me crazy, anyone experience something like this before?

[mneleventhirty]

Oh and hi to the members. Posting a picture of my DD 2001 G20, to see if this will entice someone to answer