Join Date: Feb 2009
Location: Saskatoon, Saskatchewan, Canada
The ECM has two primary methods of adjusting for idle speed - airflow (throttle) and timing. However, it has limitations for how much it can adjust, and, if one of them is just too far out, it can oscillate like that. The first two things that I would look for are a vacuum leak or a dirty MAF sensor. Seeing as you have a (presumably oiled) rotofab intake, it wouldn't hurt to give your MAF sensor a good clean. The sensors aren't very accurate at low airflows (hence the combination of MAF and speed density lookups for fueling at lower RPM), and a buildup of filter oil or anything else can have a significant effect on idle, while it gets better while under more throttle. I cleaned mine last night and it made a huge difference in fueling and has actually turned me away from oiled filters. You should also check to see if you have a vacuum leak that might not be big enough to trip a check engine light, but could affect idle. However, the most impactful thing that you could do is scan it with an OBD2 scanner and check to see what your fuel trims and O2 switching look like. Large positive fuel trims mean that it's having to put in a lot of extra fuel, either due to unmetered air (vacuum leak) or a contaminated MAF sensor that is reading less airflow than is actually flowing through. If the fuel trims differ greatly between the two banks, then the issue is something further downstream, possibly an O2 sensor. There are many further steps to track down the issue (failing MAP sensor, clogged catalytic converter, misfires that aren't being picked up by the misfire monitor, etc.), but the MAF sensor and vacuum leaks are what I'd personally look into first to eliminate them as the culprits.
2009 PBM G8 GT
TVS 1900 Maggie w/2.8" pulley (9-10 PSI), Maximizer LTs, High Flow Cats, LS9 injectors, Rotofab CAI, LC-2 WB, 40A KB BAP, TR6ix plugs, self tuned [250+ flashes], Camaro Paddle Shifters, UPR catch can, 4300k HIDs, Remote Start Heated Seat Control Module
, Aeroforce Interceptor Gauge, JBL GTO628's, JL 8w3v3's w/JBL P180.2, Bridgestone RE-11 tires