Hi all-- I recently (as of about ten days ago) bought a 2007 Prius from Steve's place, Autobeyours. It took me a while to work out the kinks, but I've been able to extract some pretty good mileage out of it once I got the tires pressed up properly and read up on how to stretch the fuel just a bit further, especially with SHM and similar techniques. However, I've noticed an issue with SHM - I know that in theory one holds 14IGN/18TPS on the scangauge at (insert your low 50's MPH speed here) to hold the fuel consumption meter at roughly 1.5x speed or better, which I have seen plenty of times. However sometimes I've found it completely impossible to hold 18TPS for more than a second or two - it'll suddenly and inexplicably jump to 21TPS without the IGN changing or my foot moving at all. And when I try to back off the accelerator, it instead drops into warp stealth, with 5IGN and 14 TPS . Given the largely flat areas I drive on and already lower-end speeds I drive, it means I have to re-accelerate in a hurry and it costs me a bunch of mileage. Here's a couple shots of the fuel consumption display - on one day, the car behaved properly, and on the other, 18TPS was impossible to hold. Mind you, this was over the same stretch of highway: This is with the Prius behaving properly: And when 18TPS was impossible to hold: One thought: I considered the possibility that driving at night would increase the electrical load (headlights, etc.) and potentially put further load on the hybrid battery's SoC, but figured the warmer temperature might mean the fuel economy was a wash? Does anyone have any thoughts/known causes of the Prius being unwilling to hold 18TPS and instead jump to a higher number (and burn much more fuel)?