Please note that I am not a mechanic, but have some mechanical abilities.

At the suggestion of a mechanic aquaintance, I took my LS to a repair shop for a diagnostic, given a rough idle. No codes were revealed as a result of the diagnostic. On the mechanic's suggestion, carbon deposits were removed from the intake manifold and the idle was stepped up. This seemed to work for a few days.

However over the course of several days following the engine has apparantly found its way back to the old idle when running hot. By hot, I mean after 15 minute drive and when stopped. At these times I can detect the engine switching from one "mode" to the next. This is when the idle drops and the car starts to tremble slightly [idle occurs at the very first line of odometer]. Other than that, the car generally drives strong.

Both mechanics suggested this is not due to engine wear but something else.

I mentioned the oxygen sensor and idle speed regulator to the repairing mechanic but nothing was checked on these since no corresponding codes were brought up with the diagnostic.


NOTE: CLEANING IAC SCREEN FIXED THIS. ALSO MEANT RESETTING IDLE.
WAS FOOLED INTO THINKING IT COULD BE SOMETHING ELSE BUT IDLE SET TO "CLOGGED" SCEEN WAS SO FAR OFF -- IT WOULDN'T HOLD AN IDLE AFTER CLEANING.