2007 Silverado 4.8L (E38/T42); 72mm Turbo, turbo cam, 88lb injectors, walbro 450lph in tank, 4L80E
I've been running in MAF only mode for over a year. I made 518HP and 551lb-ft at the wheels. Power tuning was a breeze with the MAF. As I ran out of Hz on the MAF I decided to increase my intake tubing to 4" and switch over to a card MAF. At very low airflow the MAF is OK at best so idle and cracking the throttle had room for improvement. Tuning the MAF for the new larger tubing was fairly straight forward.
In an effort to smooth out the low throttle response and idle a bit, I upgraded to the COS 2-bar OS. I now failed the MAF to tune the VVE. With a combination of the GMVE PID, and the formula to calculate GMVE using my WB02 for error correction, I was able to rough in a VVE table. Sure its ugly but it got me started. After about a month I am still chasing my tail with a surging idle issue. I've messed with everything from the PI (proportional, integral) controller to the min idle air to no avail. By accident, I set the low idle areas of the table pig rich and left it in open loop and to my surprise the idle was smooth as silk ~12.5:1 AFR. The moment I start multiplying by half % correction values back in the idle area, the surging starts again. Even if I simply use bi-directional to disable Adaptive Idle spark, surging starts. Seems no matter what I do, the closer I get to the correct values for VVE, the idle starts surging like crazy even in OL.
I am honestly at a loss as to where to go in the tune and am starting to wonder if its a mechanical issue (bad Throttle body, vacuum leak, etc) but I seriously doubt it. Who knows, anything is possible. Any suggestions on how I can baseline the idle?
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