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Old 04-16-2006, 01:11 AM   #1
Procyon
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Join Date: Jul 2001
Location: Carrollton, TX
Vehicle:
2002 WRX
PSM

Default Looking for opinion on poor idle with A/C on

Car: Well maintained 2002 WRX 5spd with no mods. ~ 42k miles.
Problem: Poor idle quality when A/C is on.

This started a month or two ago. Noticed it while sitting at a stop light with A/C on and foot on brake. When the A/C cycles on, the rpms will drop and the engine will stutter a bit, car will shake, and eventually make it back to 750rpm. This is with the car fully warmed up. If it was a little bit worse, I think that it would definately stall. If the A/C is off, the car will sit there and idle fine at 750 rpm. No other issues noticed during normal or spirited driving. Cold idle seems ok.

Brought it in this morning to get new tires and see what they thought about the idle. (still under 5yr warranty and hoped it might be covered) After a 2nd test drive they said they noticed the idle issue. However, tech thought that most WRXs do this a little normally. Mine was only percieved as being slightly worse. Suggestion that I received was to let them do a fuel system flush ($130) which would be considered maint. and not warranty. If that didn't help then move on and take a look at the IACV.

Now, IMO, this is not a fuel delivery problem. If it was, why would the car be ok idling w/o A/C or when I accelerate hard? Fuel filter is fairly new. Probably not an ignition issue either. It seems like an air management issue to me. I spent some time searching this forum and have come up with a few ideas:
1) IACV is gunked up or otherwise malfuntioning
2) Air intake leak somewhere
3) Poor ground. Candidate for ground mod. (yeah, I know this is controversial but for a number of people this seems to have fixed idle problems.)

2nd opinions on the above would be very welcome.
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Last edited by Procyon; 04-16-2006 at 11:48 AM.
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Old 04-16-2006, 01:14 AM   #2
specialev
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Location: Auburn, Wa
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07 SV650

Default

Having the AC on saps a lot of power. It was really designed to work best when the car is moving and you have the RPMS to suport the draw. You could always get a little bigger alternator, or perhaps yours is on its way out. You should see what it is making at idle compared to, say, 1500 rpms.
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Old 04-16-2006, 01:20 AM   #3
Mulder
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15 WRX/05 GTO

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I'd suspect the IAC as a likely culprit as long as the car runs ok otherwise. When the compressor turns on the ECU commands the idle slightly higher, if the IAC is sticky it won't respond properly.
There could also be an issue with the electrical load if there are poor connections someplace or the battery and/or alternator are weak.
Good move declining the fuel system flush, not necessary and just the dealer trying to take your money.
BTW this type of issue would NOT be covered under the 5/60 powertrain warranty, but only under the 3/36 bumper-to-bumper. The powertrain warranty only covers the internal engine and drivetrain components, not external accessories. Example- if you throw a rod it's covered, if your alternator fails it's not.
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Old 04-16-2006, 11:44 AM   #4
Procyon
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Quote:
Originally Posted by specialev
Having the AC on saps a lot of power. It was really designed to work best when the car is moving and you have the RPMS to suport the draw. You could always get a little bigger alternator, or perhaps yours is on its way out. You should see what it is making at idle compared to, say, 1500 rpms.
Don't quite see how a bigger alternator is a solution. The A/C is driven by the accessory belt. AFIK, the only electrical power used by the A/C would be a small amount for the electromagnetic clutch.
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Old 04-16-2006, 11:50 AM   #5
Kantalias
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Platinum Silver

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Quote:
Originally Posted by Procyon
AFIK, the only electrical power used by the A/C would be a small amount for the electromagnetic clutch.
And the electric fan, of course...but the compressor itself is not driven by the alternator.
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Old 04-16-2006, 04:25 PM   #6
Procyon
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So, does everyone agree that this is not a fuel delivery or ignition problem?
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Old 04-16-2006, 04:32 PM   #7
wrxfactor
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Location: Shrewsbury, MA
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2002 WRX w/ JDM STi
6spd, EJ255, VF39 & EWG

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Quote:
Originally Posted by Procyon
So, does everyone agree that this is not a fuel delivery or ignition problem?
The problem I'm having with my JDM WRX motor right now has to do with timing, and it has a very rough idle to the point where it almost stalls out, so there is a slight chance your timing is off or you have a spark plug problem, but I'm not sure.
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Old 04-16-2006, 04:32 PM   #8
kheff46
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yes, here.
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Old 04-17-2006, 03:44 PM   #9
rebos123
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evoIII 16G

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my 2005 wrx has done the same thing ever since it was new. I just live with it..
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Old 04-17-2006, 05:42 PM   #10
xplane
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+1 for checking your alternator or batery....
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