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Old 12-18-2008, 12:10 PM   #1
Gr3en
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Default Strange revving issue at standstill???

This morning I was sitting at a stop light and my car was jumping up in RPM. I put it in neutral and it was going from 2000 rpm back down to 1500 then up and down again. It did this till I turned the car off and on. I think it may be the IACV but I have an 05 RS and I do not think I have an IACV. Is the throttle positioning sensor? The car warm warmed up from driving 20 mins prior.

Any ideas?
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Old 12-18-2008, 12:23 PM   #2
Legacy777
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You have an IACV. It's a stepper motor/plunger on the throttle body I believe.

Sometimes they just hiccup. Just monitor it and if it happens again, it's something you should probably look at.
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Old 12-18-2008, 12:39 PM   #3
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It has happened 4 times in the last week and a half. I will clean it out and replace the rubber gasket tonight.
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Old 12-18-2008, 01:17 PM   #4
Qman
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Josh is probably correct is his thought. But, check the temp sensor as well. A faulty reading will cause erratic idle.
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Old 12-18-2008, 01:43 PM   #5
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YES! someone else with the same problem. I've experienced it numerous times as well. The jump in idle RPM has only been noticed when the A/C compression kicks on. Normally it jumps up to 900 RPMs or so when compressor kicks in, but when it is acting up it revs to 1500RPM or higher. Have logged and logged and logged, ECU is adding throttle, have no clue why.
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Old 12-18-2008, 08:40 PM   #6
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Any input is appreciated.
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Old 12-18-2008, 10:10 PM   #7
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Quote:
Originally Posted by LTracer View Post
YES! someone else with the same problem. I've experienced it numerous times as well. The jump in idle RPM has only been noticed when the A/C compression kicks on. Normally it jumps up to 900 RPMs or so when compressor kicks in, but when it is acting up it revs to 1500RPM or higher. Have logged and logged and logged, ECU is adding throttle, have no clue why.
Keep in mind that the windshield defrost setting will use the A/C compressor to dry the air, no matter what the thermostat knob is set at, so you may notice high/fluctuating idle with the windshield defrost selected and the fan speed set to anything besides 0 (zero).
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Old 12-19-2008, 12:30 AM   #8
LTracer
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Quote:
Originally Posted by RaceFaceXC View Post
Keep in mind that the windshield defrost setting will use the A/C compressor to dry the air, no matter what the thermostat knob is set at, so you may notice high/fluctuating idle with the windshield defrost selected and the fan speed set to anything besides 0 (zero).
Yes, I'm well aware of this. Problem is the idle fluctuates much more than normal on random occasions. As I said normally it rises to 900-1k or so, when it's acting up it will hit 1500-1700 quite often. This issue only surfaced in the past 5k miles or so.
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Old 12-19-2008, 02:37 AM   #9
MrZDeere
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I have the same issue in my '08' and I'm not sure why, it's done it randomly for months and very frequently. Do you think it's worth taking to a mechanic for it or is it no big deal?
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Old 12-19-2008, 09:01 AM   #10
Gr3en
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LTRacer. I had changed out my front O2 sensor and that fixed the issue. The stealership was shrugging their shoulders so I suggested a new front O2 and it worked. Thank God for Subaru of Schaumburg. There service is open till 10:30.

Edit: I had to bring it back to the stealership. It is now the rear O2 sensor.

Last edited by Gr3en; 12-19-2008 at 07:14 PM.
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Old 12-20-2008, 01:36 AM   #11
formula91
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Weird, I don't have that huge of a jump when my A/C or fan kicks in. I know that I don't pass 1k RPM at idle when I'm warmed up at the very most.

I don't understand why the 02 sensor would make the car add throttle. I though it only had authority over fueling. My O2 sensor is running just fine.

What sensors have control over the throttle? Thermostat? MAF? Both of those if malfunctioning would give other symptoms. Perhaps the throttle gate is loose. (?)

BTW local Subaru-er. Did you drive today in the morning before the plows got to it?

I went out at 1 AM to screw around. It was awesome. lol
They said it would have been up to 12 inches. What a lie.
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