Self reving

[Patrick1234]

I have a 2009 Toyota auris 2l d4d and I have noticed at times that she would rev half a tick more than normal at times.. it's probably not a major issue but just out of interest what would it be.. there is 5 ticks from 0 to1000 rpm.. normally she sits at 800 rpm when ticking over even when cold but lately I've noticed she sat at 900 rpm for quite some time then again (on a different day) the same thing would happen but it may not last just as long as the last time.. now I have lights, heater, radio and basically everything electric off so I don't think it's that. So why would an engine do that? The throttle isn't Ricky either!?!?! Lately I'm having trouble with the Battery light and fuel filter warning light (the filter is ok) but I narrowed that down to a faulty altenator.. would that explain it?? Again I'm just asking out of curiosity (don't need cheeky comments)!! Thanks.. 

[mrfixer]

The ECU will command the engine rpm to increase if there is additional load...  e.g. additional electrical load or low Battery voltage, air con, power steering..

[furtula]

You said your alternator is charging at only 12.2 or so volts. So the Battery has to make up for the rest during idling time esp if you have lights, power steering, radio etc on.

I'd say the car is making up by higher idle, try turning everything off, the rpm should drop.

You need to replace the alternator anyway, better to do it now. With Auris being power steering, i dont know what would happen if the alternator would suddenly die and the car would be run by Battery with not even a full charge.