K11 intermittent high idle looking for help diagnosing

Hi all.

My 94 PreFL has a intermittent high idle, while not dangerous ( as in moving the car in D with no throttle input ) it is enough to have me concerned.

I replaced the throttle body unit with a new one from eBay in July 2016 and have done close to 20k since with zero issues.

Before I go spending the money to have another TB unit I am concerned it may be something else to blame? my reasoning is

1. zero stuttering when even on the fast idle

2. No running rich this was a major problem before I replaced the throttle body unit in 2016.

Any suggestions will be appreciated.
Thanks, will be checking for vacuum leaks when the rain stops using some WD40, if that comes up blank, will look into the lambda sensor too.

edit: Anyone knows a solid source for a branded sensor? may get a new one ordered anyway just to be safe as the one on the car looks very old.