Holley sniper EFI motor suddenly revving uncontrollably when I blip the throttle

[RockinRobin]

Can also verify that temp sensor is staying wet all the time. We ditched the sniper for sequential. I cannot understand how you open the throttle blades for initial start up and then go back to zero when you verify.

Because I don't open the throttle for start up. I simply hit the starter button and it starts. Anyway the reason has been discovered and solved. Secondary butterflies were sticking open in their bores.

 

[BillGrissom]

^^This, "back to basics." An engine MUST have AIR to rev. Whatever the sensors/ electronics/ fuel ratio is off the table, it MUST be getting air someplace. The big difference between EFI and carb is, that if you have an air leak, the O2 will crank up the fuel. But the AIR is what drives it.

Vacuum leak, PCV, loose "somethings", IAC is AFU, stuck throttle blades/ linkage, etc etc.

Very true about basics. In EFI engines, the O2 sensor has only limited authority on fuel flow, something like +/-10%, termed "fuel trim" if using an OBDII adapter (1996+ vehicles). If the common MAP sensor type controls, the controller adjusts fuel based on engine rpm, and intake manifold pressure, plus a few other sensors like IAT and TPS. That is an "open loop" prediction, like say an initial setup to fire an artillery shell. The O2 sensor is like a "forward observer" who "feeds back" corrections until "on target". Thus, an intake leak should be automatically compensated for. Try it by pulling the vacuum brake booster hose. The engine will idle much faster, but still correct O/F ratio. If the less-common mass-flow sensor (mostly Ford and Mazda?), an intake leak doesn't affect the "open loop" prediction since after the mass-flow sensor. If more than 10% extra fuel is needed (all O2 sensor input can correct), the engine will run lean. I assume the Holley Sniper uses a MAP sensor, so should compensate for vacuum leaks.