I recently chased an issue with getting lean spikes on my Holley system. Long story short, it turned out to be a distributor problem causing intermittent trigger failures to the ecu. I have a DUI (Davis) tfi distributor. The hall effect pickup is made of plastic and slips over the shaft and held in place with a pin. The fit had gotten real sloppy and it was moving all over the place. I made up some shims and reassembled it using some epoxy to make sure it stayed secure and it works like a charm The car runs better than it ever has. So, be aware that misfires can show up as lean spikes. Which also leads me to another point that EFI is blamed for a lot of problems which are actually caused by some other component, or tuning itself. Like all computers: Garbage in = garbage out.