My MM was outdoors overnight, last run was yesterday afternoon. This afternoon I fired it up and paid close attention to the RPM.
Instant rev to 1800-1900, hangs there for about 5-10 seconds, then drops to 1500. If the A/C is on, the compressor then kicks in at that point, and RPM drops to maybe 1400.
Then it gradually settles on 1200. After a minute, it will drop to a cold-sounding 1000-1100.
Just for kicks, I revved it to 2500, just to see what it would sound like. Man, if my car fired up to 2500 on a startup, not only would I be surprised, I'd be asking questions. I know these are modern engines and all, but 2500 is pretty high for a startup. What's especially disturbing is all the talk of knocking at startup... yikes!
2500 sounds cool on startup, but not even old high-internal-friction V8s would rev that high on startup. In fact, most old 4 barrel carbed engines would end up activating the primary circuit on the carb if they tried to cold-idle at >2000 RPM, causing "nozzle drip" from the primary circuit which in turn would wash out the cylinder walls and increase wear. Now, this won't happen with an EFI engine, but all this to show that 2500 is pretty damned high for a startup.
Even 1900 is kind of high for an EFI V8, to be honest. My GTA, stone cold, will grab maybe 1200-1400, 1500 on rare occasions, and almost immediately settle to 1000 RPM. My WS6, after having sat all week, fired up this evening to a snarly 1300 RPM, then almost immediately dropped to 1000 RPM.
What do Mustang 4.6s do at startup?