Sticky Throttle Cable - High Idle Issue

Hey guys! Recently bought a dc2 and it seems the car has an intermittent sticky throttle body cable problem. Used the search function but could only find high-low idle problems or problems with the TB sticking when accelerating

Bit of a background:
During one of the inspections prior to purchasing the car, the car was sitting on high idle (around 3k rpms) and as a result I didnt go ahead with the sale on that particular occasion. However, the seller got his mechanic to come around and "fixed" the issue as he said all that needed to be done was to tighten the nut connected to cable. Thought all was well as the high idle had gone away and bought the car.

But in the 1 month period since I bought the car, the problem has come up two more times and both times have been where the car has been driven to around 5-6k rpms (Note: Haven't vtec'd the car much at all cause I still need to convert my P plates to manual).

I can easily resolve the issue by tugging the cable down and restoring normal idle but does anyone know what the underlying problem is? Essentially can't drive the car hard at all if I want to avoid the problem :S
I've attached some photos to explain what I mean.

Attachment 27783
What the cable should look like. should return to this position after accelerating.

Attachment 27784
Position the cable was stuck at, causing the butterfly valve to be stuck open and the 3k rpm idle.

Check the path that the cable follows from firewall to throttle. Make sure there's no sharp turns or if it's pressed against something.

The obvious thing would be that it's just stuck inside somewhere with corrosion or other. Take it off and see how freely it moves.

Take off the throttle intake arm - open the throttle from the cabin or with your hand - open the throttle body full and spray abit of carby cleaner in there. Grab a old tooth brush and scrub scrub inside.

Hopefully this fixes your sticking throttle issue

Thanks for the replies guys (Y) Will let you know how everything goes!

Discount the throttle cable, move with your hand to see if its tight, if it feels nice and lose, move onto the throttle body and check if the return spring is dirty, clean it with some degreaser.