Possible reasons for engine idling higher, and "auto revs?"
September 17, 2013 6:02 PM Subscribe
Carfilter: Car had been running fine all summer. Saw a bit of this yesterday, more during today's commute. Engine idling slightly higher and it revs itself at rest. Otherwise, it runs normally under load.
posted by porpoise to travel & transportation (6 answers total)
It's an old B16A3 in an '95 manual transmission Honda del Sol. Normally, it idles at ~850rpm. Now, sometimes at rest, the engine idles at around 1100rpm but spontaneously fluctuates up to 1250rpm over a couple of seconds, backs down to 1100rpm over a couple seconds, fluctuates up to 1250rpm over a couple of seconds, &c.
Sometimes it'll go back to idling steadily at ~850rpm.
Otherwise, the engine behaves and sounds "normally" when under load. Have not noticed any dramatic difference in gas mileage or smell or torque. Mostly city driving with variable traffic.
Have not changed octane or source of fuel recently. Currently just under half a tank of gas. I don't think that this behaviour correlates with engine temperature/warmed-up-ed-ness. There's an aftermarket radiator that keeps the engine at or below 50% on the gauge no matter how adverse ambient/driving conditions have been. Ambient temperature has moderated but its not extreme (averaging 20'C instead of 25'C) but average engine temperature ~30% instead of ~45% on the gauge. About 5000km since last (synthetic) oil change, next recommended change at 7000km.
What could be some possible reasons for this sudden behaviour, is this a sign of imminent demise, and is the situation likely to become worse? I'm not sure if this behaviour is always replicable.