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Hello, I’m having a terrible time getting idle tuned. I’m have trouble with surging. This is a new build. 408 ci. Holley hi ram intake. Holley 105mm tb. Ve table is very close. Idle rpm target is 850. Maf is failed. Timing is about 22 when it’s not surging. Base running airflow has been increased. I’m trying to understand what the surge is caused from. Using the scanner, I locked the timing at 15. It did settle down but not 100%. Any advice on troubleshooting this? Thanks
Surging is caused because the torque at one operating condition exceeds the amount needed for steady idle. The engine then accelerates to a new condition, where there is insufficient torque to maintain a steady idle, so it decelerates, and the cycle repeats.
At idle, we don't run MBT timing, so more timing will increase the torque at a given operating condition, and less timing will decrease the torque. You say your VE table is very close, so I assume that means we don't see much mixture variation when it surges (that surprises me, as usually we find that as the manifold pressure decreases with increased RPMs, the VE won't be tuned (since we don't get to that condition usually). If that is happening, try increasing the timing at the max surge RPM until it holds the idle there. Now see if you can adjust the fuel (VE) for that condition).
Now your idle air control is probably also contributing to this, so you might be tempted to get the engine to idle without it initially (disconnected and set to closed), and when tuned, re-connect it and just let it add air when the Idle drops too low and is trying to stall.