Low idle problem

[powderhound]

Greeting yall.

Recently my 98 legacy has started idling weird. It will idle normally at 700 rpm and will drop at random to 500 or below. I can feel it and I think the car is going to die...it doesn't but I give it gas out of instinct. The crankcase is currently overfilled slightly but its not loping at idle like it does if its really overfilled. I'm thinking it could be a vaccum leak or the IAC but not sure where the IAC is or how to nail down a vaccum leak. Any ideas? TIA.

[blitz]

Check for dry, cracked, or dislodged Vacuum hoses.

 

Also, when is the last time you've (ALL three):

 

1. Cleaned the TB with TB cleaner and a toothbrush?

2. Cleaned the IAC valve?

3. Cleaned or replaced the PCV valve?

 

These are the three calibrated air-orifices that the engine draws air through at idle. When (NOT IF) they get crudded up, the engine can't meet the computer target count (idle speed calculation), and it starts flipping out.

 

Are you getting a CEL?

[powderhound]

Thanks Blitz.

 

I have never cleaned the throttle body or IAC not sure where either is. I guess at 130K they might need it. Recommended cleaner?

Replaced the PCV at 103K when I had the front end resealed. I used a fram PCV valve and looking at it yesterday looked to be in worse shape than the one I replaced. Maybe I should splurge for OEM?

 

And there are lots of vacuum hoses to check I was hoping there was some magic trick to nailing it down.

[blitz]

Thanks Blitz.

 

I have never cleaned the throttle body or IAC not sure where either is.

Remove the airbox. The opening where the air enters the engine is the throttle body. Open the throttle with one hand and spray little jets of cleaner into it, then scrub the dirty black areas with the toothbrush, repeat until the black areas are clean, bare metal again. Use a flashlight. To prevent flooding the intake with cleaner, start the engine briefly, then continue.

 

The idle air control valve is mounted on the top of the TB with a couple of small screws. Take it out and clean the appropriate parts with a Q-tip soaked in cleaner, don't spray the whole thing. Also spray the orifices in the TB that the IAC plunger resides in.

 

I guess at 130K they might need it.

I do it every summer as part of normal maintenence.

 

Recommended cleaner?

Any name brand throttle body cleaner. If it dosesn't dissolve the toothbrush, it's better.

 

Replaced the PCV at 103K when I had the front end resealed. I used a fram PCV valve and looking at it yesterday looked to be in worse shape than the one I replaced. Maybe I should splurge for OEM?

Subarus have quirks, so I use OEM parts on my Subaru. There is no basis in fact for that, just a gut feeling about it. Other vehicles I've owned (Ford, GM, Mitsubishi) I'd always used aftermarket parts.

 

And there are lots of vacuum hoses to check I was hoping there was some magic trick to nailing it down.

Neither hope nor magic tricks play any part. Either you're willing to systematically diagnose your way through a problem or you'll have to pay someone else to do it. Are you getting a check engine light?

[powderhound]

Blitz thank you. I have no CEL but that doesn't mean it's not throwing codes. It may be a couple weeks till I'll be able to clean it...do I risk any damage? I believe 500 rpm is within spec but it feels slow to me...and it has started dropping below 500.

[BlueTrain]

ya, don't replace any of your parts with anything by Fram... bad stuff.

i'm not sure if your car has an egr valve, but if it does, id check that as well.

im currently in the same boat (low, shaky idle when warm) so i know how it feels. hows the fuel filter.. a partially clogged one can cause a low idle too.

[blitz]

Along with Blue Train's suggestion I'll add that you could also be having an intermittent connection developing at one of the underhood connectors. I'd tend to think something like that would throw a CEL, but generally a fault has to be present continuously for some specific time interval before a code is thrown. I'd be surprized if you haven't got a code logged at this point.

 

Clean all the gunky stuff first (including the EGR), before moving further. Don't make things more difficult for yourself than they really are.

[powderhound]

So now the idle is high--1000 rpm and it thew code P0507 Idle Control System RPM higher than expected. No kidding I was watching it idle at 1000 when the light came on. So I bought some Valvoline synthetic TB cleaner. I'm still wondering where the IAC is located. And being the fan of Seafoam that I am I've seen some threads describing a procedure to use vacuum to run seafoam through the TB. What would be the prefered method of cleaning these parts? And any theories why it has shifted from low idle to high? Is the ECU over compenstating for something it learned when idling low?

[Spazz698]

And any theories why it has shifted from low idle to high? Is the ECU over compenstating for something it learned when idling low?

 

My car is doing the same thing- after fixing the same problem your's had too lol. I fixed this in class (I'm getting ase cert ) after a good 2 hrs of cleaning, putting stuff back on, reconnecting hoses and trying to figure out why it went from a low sporaddic idle to a steady high idle, we (my teacher and I) put this on hold til he gets ahold of a friend of his who works for subaru cuz we've done everything we could and it just wont idle where it should, so he's starting to think its one of those subaru things.

[powderhound]

Let me know what you figure out. I have not cleaned mine yet and it has switched to high idle. Have you looked for a vacuum leak? Maybe you should try disconnecting the battery to reset the ecu.

[Setright]

I'd just like to chime in and thank Blitz for offering top quality advice!

[powderhound]

Setright I've been waiting for you to chime in in more substantial mode than that. So here's the latest:

 

I cleaned the TB and sprayed cleaner into the hose going into the iac (couldn't figure out how to get it off).

 

There was oil in the hose going into the pcv valve.

 

I put a new oem pcv valve on.

 

Now the car idles and SLOWLY creeps its way up to 1000 and then drops back down to 600 and starts climbing again. I'm lost.

[beezer]

I have a 1st gen. legacy 2.2, and I don't know how much has changed on the engines over the years.

 

I had a similiar problem where the car would act much like yours does. I would get the code for the air control valve. What I would check, is the spark plugs, are they seated properly, what is their condition like. Make sure the wires are OK. When the engine is acting funny start pulling the wires 1 at a time to see if it affects the car at all. Also check the knock sensor, mine was cracked and was sending miss information to the computer, it didn't show up as a fault code though. I think it sounds like more of a electrical problem, either spark related or a faulty sensor.

 

Hopefully this might help, I scratched my head for a couple months with my car.

[Setright]

Sorry powderhound, but I would have gone through the same points as Blitz, and I was in a hurry :-)

 

Having said that, the symptoms you describe now don't sound like clogged hoses. These would just cause erratic idle, not the systematic up and down you are experiencing.

 

I think you need to remove your IAC and clean it thouroughly. Not sure what type your 98 model uses. Is your air filter nestled behind the headlight or just behind the throttle body?

 

IAC must be causing this. The engine runs fine at speed right? IAC is the only thing that would cause the up/down idle. Or heaven forbid, the ECU could be faulty.

Gunk in the IAC would cause it to stick and react much slower than the ECU expects, which is why the idle doesn't run wild, but just isn't stable.

 

Very old spark plugs might play a part, but I think you'd get rough running at higher revs too.

[powderhound]

Thanks guys. The spark plugs are new but the wires are still original. I want to take the iac off and clean it but am not sure how to do so. Do I need to take out the two little screws that go into the gray part and are perpendicular to the ground or is it the two longer bolts that are parallel to the ground. If someone has detailed instructions/pictures for removing the iac that would really be sweet.

[blitz]

Remove the two vertical screws on top, then remove the assembly. They may be siezed into the aluminum TB, so you may have to keep them wet with PB blaster for a couple days prior to coaxing them out (DON'T MUCK-UP THE HEADS :-\ ). The other two screws on the side are some oddball-sized, 5-sided, torx-type headed things. That tells me that Subaru doesnt want that motor sub-assembly removed for just any reason.

 

A small amount of coolant may spill when the valve is removed on account of the TB being heated by coolant running through a passage there, so before removing the valve, open the throttle fully and stuff a small rag between the top of the open butterfly and the TB bore. That'll catch spilled coolant from going down into the manifold. There's a rectangular o-ring between parts, don't lose it.

 

After all this cleaning is done and everything is re-assembled, reset the ECU.

 

None of this may cure the problem, but it's important to have this stuff clean and it remains step #1 before moving on.

[beezer]

Sorry, I realized later that I probably should have better explained myself. My particular problem was intermittent, for some reason I assumed yours was too.

 

Other than the idle problem does the car behave normally?

Will the car ever idle properly or is the CEL always on?

 

Like others have said, first try and rule out, or pin point the problem is the IAC. I would hazard to guess if your car will behave properly on occassion that the IAC isn't the sole problem. If the CEL is always on and the car always idles poorly then the IAC is probably part of the problem. The only point that makes me wonder is that the idle changed so differently when you replaced the PCV. Oh well, clean the IAC and see where you are.

[powderhound]

Yeah it's running fine otherwise and the cel has not come back (yet).

So..ummm..I f'd up one of the screws on top of the iac. Not sure I can ever get it out now. Maybe I can soak it and grab it with some pliers or drill it?

[Chef]

Get one of those stripped screw removal bit sets from Sears or some other hardware place, and try those. Or can you grip the top with vice grips?

 

Definitely use some penetrating oil to help.

 

 

Yeah it's running fine otherwise and the cel has not come back (yet).

So..ummm..I f'd up one of the screws on top of the iac. Not sure I can ever get it out now. Maybe I can soak it and grab it with some pliers or drill it?

[Setright]

BEst way to get a seized bolt out is to drill a small hole into it and insert a left-threaded "bolt extractor". As you turn this counter-clockwise it will screw itself into the bolt and hopefully the bolt start to move.

 

Avoid drilling the hole bolt, as you will damage the thread, and have to used oversize bolts to reassemble.

[Spazz698]

hey, ok the first thing I did check was for vacuum leaks (Im so happy i have access to that machine, it makes it so much easier) none. after cleaning everything up (the oil in the pcv valve after cleaning is normal I was told, mine had oil in it too) my teacher decided to play with some of the plugs and managed to get it to idle steady at 2k- dont ask I dont know. We adjusted the throttle down to 1000-1200 cuz apparently that IS adjustable, damn subaru and their lying ways lol. Anyways after giving up for the night and driving home, the idle actually dropped to 700 where it should be. It's been there ever since. But Im not saying the problem was completely fixed since the idle still drops occasionally, but it's so minor... it's just one of those things a driver would pick up if they were mildly obsessed with their car