I've had this happen intermittently on my 2003 Prius for a few years now: When I turn the ignition to Start instead of revving directly up to idle it seems to pulse to high RPM and back down. It's about one pulse per second and either one or two pulses before the engine stays running. So it seems like the car is having trouble starting the engine, but from the sound of it I'm pretty sure it's revving under gasoline power and not just MG1 spinning it up. I haven't noticed a pattern to the conditions when it does this (can happen on warm and cold starts). I estimate the pulsing happens about one out of every four starts. As far as I know there's never been any code stored related to this, but it seems odd. Does this happen to anyone else?
I've noticed odd rev-up (albeit with a 3rd gen) reliably, after a 12 volt battery disconnect. For the next two-three starts. My speculation is it's "relearning" something, maybe throttle response. Could battery be ailing?
I think the battery is going on 4 years old and I don't drive often so that's quite possible. I'll do some investigation, and if it does the same thing consistently after disconnecting the battery that'll be an indication to replace it.
My hunch is to check the engine air filter, and clean the MAF sensor (although IIRC a dirty MAF sensor will set a code). BTW, “ normal” idle speed on my ‘02 is 1280 rpm.
Being intermittent and ongoing behavior, if it's a 12 volt supply problem, also possible it's a loose connection somewhere.
