YACT: Check engine + rough idle after sitting for the better part of 2-3 months?

Viper GTS

Lifer
Oct 13, 1999
38,107
433
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Car in question is a 1995 Subaru Impreza, 1.8L H4.

I've been travelling for work & have spent the better part of the last 2.5 months on the road. My car has been sitting all that time, driven only once when I was home for a couple days.

Today I started it up, it's idling very rough + the check engine light is on. Also the idle speed jumps from 1K to 2K and back again with no throttle input.

Do I just need to let it run, or is this something I need to worry about?

Viper GTS
 

Heisenberg

Lifer
Dec 21, 2001
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I hope you changed the oil after letting it sit that long. Anyway, sounds like a problem with the idle air control (or whatever Subaru calls it). It may unstick itself after a while, or it may need to be looked at.

Edit: Could be due to the gas going bad, but IIRC it usually takes longer than 3 months for that to happen.
 

jlee

Lifer
Sep 12, 2001
48,518
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Old gas, maybe..?

I'd let it run a while - the Corolla I had ran a little rough for a minute or two, after not running for weeks.
 

NutBucket

Lifer
Aug 30, 2000
27,103
596
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Could it be something as simple as a stuck PCV? I say you give it a full tune up and report back.
 

BCYL

Diamond Member
Jun 7, 2000
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I would recommend changing the engine oil, then let it run for a while...

Was your gas tank empty or full when you left the car? It is always best to leave the gas tank full so there isnt room for condensation...
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
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Haven't checked anything yet, though there is no evidence of any leakage. I've let it sit for over a month before without incident.

The gas that's in it shouldn't be bad, though if it is I intentionally left it nearly empty so I could fill it with new gas. As for leaving the tank full, I had no idea how long I would be gone so I didn't want to put a full tank of gas in it... It is freezing ass cold outside, so condensation is a definite possibility.

Assuming there's no pool of oil or anything bad like that am I going to hurt it by just letting it run for a while?

I don't have time to take it anywhere or get it looked at, I'm flying out again Monday & will be gone for several more weeks.

Viper GTS
 

natto fire

Diamond Member
Jan 4, 2000
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Originally posted by: Heisenberg
I hope you changed the oil after letting it sit that long. Anyway, sounds like a problem with the idle air control (or whatever Subaru calls it). It may unstick itself after a while, or it may need to be looked at.

Edit: Could be due to the gas going bad, but IIRC it usually takes longer than 3 months for that to happen.

This would be the first thing I would check (the IAC). It is usually bolted to, or near, the throttle body, and has a couple wires and sometimes coolant lines, going to it. It can be cleaned with carb cleaner. Gas usually takes longer than that to go bad enough to cause those problems.
 

Titan

Golden Member
Oct 15, 1999
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another vote for change the oil. If it sat with a non-full gas tank your fuel could be messed up a bit as well.
 

Ronstang

Lifer
Jul 8, 2000
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Originally posted by: Heisenberg
I hope you changed the oil after letting it sit that long. Anyway, sounds like a problem with the idle air control (or whatever Subaru calls it). It may unstick itself after a while, or it may need to be looked at.

Edit: Could be due to the gas going bad, but IIRC it usually takes longer than 3 months for that to happen.

That was my first guess and it is the #1 reason a fuel injected vehicle idles poorly. The gasoline is simply not old enough to make the car run poorly and even if it was it would not cause a wandering idle.
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Were it the IAC would driving it make it come unstuck?

I have to head out in a minute (different vehicle, thankfully) but I can take a look at it when I get back.

Viper GTS
 

Ramma2

Platinum Member
Jul 29, 2002
2,710
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Change:

Oil + Filter
Fuel filter
Air Filter
Gas

Check:

Plug wires
Plugs
Belts
Hoses
Vacuum lines
 

GuitarDaddy

Lifer
Nov 9, 2004
11,465
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Run by an Autozone or other parts store that will plug in the handheld computer under your dash for free and tell you what the trouble codes are
 

DivideBYZero

Lifer
May 18, 2001
24,117
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FYI:

Locate the two ECU check connectors, for most cars they are located under the steering column and consist of a black plastic male and female connector, and a green male female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side.
 

natto fire

Diamond Member
Jan 4, 2000
7,117
10
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Originally posted by: Viper GTS
Were it the IAC would driving it make it come unstuck?

I have to head out in a minute (different vehicle, thankfully) but I can take a look at it when I get back.

Viper GTS


Originally posted by: Captain Howdy
This would be the first thing I would check (the IAC). It is usually bolted to, or near, the throttle body, and has a couple wires and sometimes coolant lines, going to it. It can be cleaned with carb cleaner.

Driving might help it, but chances are carbon has made the plunger stick. Carb cleaner gets it off really well.
 

DivideBYZero

Lifer
May 18, 2001
24,117
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If you suspect or get the MAF fail code, remove the connection to the MAF and spray Carb cleaner into it.
 

Soccerman06

Diamond Member
Jul 29, 2004
5,830
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81
How long is the idle rough? Does it go away after a few minutes? My old Bonneville had that kind of a problem and had a problem with the fuel injectures being dirty. But, if it is consistant, I would definitely change the gas and oil. The filters should be fine until their mileage expires.
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Originally posted by: DivideBYZero
Don't SPIDER this thread, dude!

No spiders, it's the gf's birthday so I have other obligations.

I only let it run for ~5 minutes, I'll try it again. It was rough the whole time, & jumping between 1 & 2K.

If it doesn't smooth out & is still throwing the CEL I can get it checked tomorrow. Beyond that I probably won't have time to get it dealt with since I fly out again Monday. I was just hoping to be able to drive it a little while I'm home.

[EDIT]OK better description of what's going on...

It idles at 2K, the CEL comes on, it drops to 1250, then it goes back to 2K & the CEL goes back off. It spends about 3-5 seconds at each RPM level, & cycles constantly between the two. It stops right at 2K and 1250, right on the nose like it's supposed to be there.

What's the verdict, let it run for longer or drive it to the auto store tomorrow & get the codes checked? It's pitch black and 15 degrees outside so I don't know how much I can do tonight.[/EDIT]

Viper GTS
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
OK, just got out there & got the code.

It's flashing 24, which means that Jack Bauer is on his way to fix it right?

Actually thanks to DivideBYZero's link I know that means it is the IAC solenoid.

I guess now the service manual I spent 20+ hours downloading & piecing together is going to come in handy since I have no eartly clue where the IAC is located (or the throttle body for that matter...).

And I guess I need to go get myself a can of carb cleaner too.

Viper GTS
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Well I got carb cleaner but I couldn't get the bolts out (too old/rusty). I finally just said "screw it" and took it for a drive. The problem seems to have gone away, & it's back to its usual self.

Should I just take it somewhere (eventually) and get the sensor replaced? Or just not worry about it unless it proves troublesome?

Viper GTS
 

Heisenberg

Lifer
Dec 21, 2001
10,621
1
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If it idles and otherwise runs okay I wouldn't worry about it. If it starts to act up and the CEL comes on again then yeah, I'd have it fixed.