I have a 2012 5.0 Mustang with a Whipple supercharger. Intermittent issue that I just can't figure out. Issue only occurs maybe 1 out of every 10 starts. The engine will idle noticeably low and make a sputtering/misfire sound if I attempt to rev over 1500 RPM's. When this occurs my boost gauge reads 28 PSI(normally 14-15 range). Cycling the key corrects the issue. Doesn't matter if it's a cold start or have been driving for awhile. Running e-85 if it matters. Thank you for any advice on where to looking?

 

just a wild guess, probably way off but just to get the thread moving: does that blower have a relief valve, that is supposed to let off the boost at idle or low throttle? if yes, maybe it is sticking sometimes?

 

, I think you may have nailed it. Seems as if the pressure is not releasing correctly all the time and that would be my first guess.