Change in idling behavior - an issue?

[Flopka]

I have a new 2012 Impreza Premium with only about 500 miles on it. It's been unfortunately subjected to a lot of stop-and-start city traffic in its young life.

 

For the last few days, I've noticed a change in its idling behavior. It will go down to about 700 rpm on idle (as usual) but then sometimes after 20-25 seconds, the engine seems to come back to life and it goes up to 800-900 rpm for a few seconds, then dies back down again. Depending on how long I'm at the light, it may go through this cycle multiple times.

 

I'm not sure why it is now showing this behavior, after a month of never doing that. Anyone know what's going on?

 

The only unusual thing that the car went through, prior to this behavior starting, was that I was stuck in a very long dead-stop traffic jam (~10 minutes) one morning.

[mattocs]

AC or defroster running?

[Flopka]

No, neither. Although that's what it sort of feels like.

 

Something else that I keep hearing now also, is a sort of soft click/vibration beneath the car on occasion - almost as if some sort of switch is coming on periodically. I don't know what that is either, and while it doesn't seem directly correlated to the idling issue, I also noticed it starting at around the same time.

 

I will doubled check to see if I have left something on. The A/C is definitely off, and I don't THINK I have the defroster on but I will check again. If it's something embarassingly stupidly simple I will let everybody know. :-)

Edited April 4, 2012 by Flopka

[ivans imports]

New car have the abillaty to learn it moniters your driveing and tunes itself acordingly probly dident understand the change in driving and ran some different maps to try and tune itself or your defrost was on or fans turned on did it check engine light ? bad gas ? did it corect itself or still doing it ?

[Flopka]

I've absolutely confirmed I have not left anything on - the A/C is off, the rear defroster is off, the heated seats are off. But while I had my rear defroster off, it appears I left the blower in the half-and-half defrost position. I'm home now, so tomorrow I'll see if shutting that off does the trick.

 

It reminds me somewhat of the A/C compressor kicking in, but is much less pronounced.

Edited April 4, 2012 by Flopka

[mattocs]

Maybe the radiator fans kicking on and off?

[95legwagon]

Maybe the radiator fans kicking on and off?

 

i would almost 99% guarantee thats what it is..... mine does the exact same thing..... its the fans kicking on....they pull enough current from the battery where the alternator puts a lil bit more stress on the engine causing the idle to drop. and it'll run the fans till its under a certain temp....then turn them off....then they'll come back on in a matter of 30-45 seconds in dead stop traffic.

[Flopka]

I promised if it was a stupid answer I would come back and admit it... Yes, the solution was very simple: turn off the damn defroster blower.

 

My previous car did not activate the A/C when you had the blower position set to defrost or even partial defrost. So, I thought there would only be an issue if the defroster button was pushed in. Wrong. Having the blower switch set even to partial defrost (even if the defroster button is not pushed) will make the A/C kick in, to dry out the air being sent to the windshield. (Actually, the A/C in my old car was broken and I never had it fixed, so it very well might have been part of that car's design too.)

 

The switchy noise also went away, so, there's the answer.

 

DUH.

Edited April 5, 2012 by Flopka