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Discussion Starter #1
Team,

The idle is already very slow (about 500) and with the brake pressed there is the shaking vibration.

I know there are 1000 reasons, but I eliminated some - ignition, booster, MAF; all the codes are OK. So I have the following question:

I narrowed it down to either fuel or air. The question is how could I detect and air leak? I can't start disconnecting each and every hose one by one, right ... I'm thinking about getting the trace on the Inlet Manifold pressure off Torque app and posting it here but is there a better way? I can't find a spec on the rated pressure in the inlet box during idle, and of course I have no idea how out the calibration a sensor that reports this can be.

I'll keep digging. Any input is welcome ... and I probably already tried that. Thanks!
 

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Is this and auto or manual?

Did you check your battery? A weak battery will do this. Same with bad grounds. Alternator working?

Another thing would be the throttle body is dirty inhibiting air flow. Could also have a bad PCV valve.

If you had a vacuum leak on this car, the idle would go up/down while the computer tries to compensate.

Does the car idle up if you turn the AC on?

Then there's the timing belt. If it's stretched out enough, the cams lag behind and you get slow/rough idle.
 

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Discussion Starter #4
Wow, guys you're great!

Just checked the AC - no, no change ... hmmm. The belt is due (I'm at 104K miles), I have the parts but have not found the time to negotiate that with the local pros (I'm actually way out - in The Netherlands), besides I keep checking for oil leaks in the belt box - because there where none I never though about any other complications or rupture risks. But I think the problem started on a hot day after few bad revs (its automatic, 2.5i, 2009 Outback) so the belt was overstressed. Oh well

Still the battery is No.1 suspect. My kids killed it at least 2 times in the last few months - "oh I forgot the reading lamp, oh you found that one on ...". These are the risks when you drive once a week.

Any Torque codes/traces/etc I should look at? Thew vacuum trace is steady as the revs dip so vacuum leak its probably not ...

Thanks again. Greetings from across the Pond!
 

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With a frequently dead battery, the idle relearn would be a good place to start, especially on an automatic.

Otherwise, you can test for air leaks with a propane torch, non-ignited. Standard torch head, very slight open valve, and wave it around the gasket and hose areas and listen for an increase in idle.
 

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Discussion Starter #7
Will do the propane thing but first will swap the battery.

I can do the belt myself but I want to piggy-back few more things:
  • I'll replace all the rollers - I got those when I was leaving US. Finding OEM spare parts in Europe is a royal pain (but they honor the US recalls)
  • I'll flush the radiator and replace the coolant. It's all 10 years/100K miles old.
  • I'm on edge for the water pump; I have no spare one, it makes no noise ... and I'm worried about a leak afterwards. Can you guys pls tell me it's not critical ? ...
  • Then I'll do all the other fluids - brake, AT, differentials. I did those at 40K ... diffs are probably still good
  • Finally will swap the spark plugs. I don't won a reliable torque wrench and that's my only concern. There is some oil sweat on the valve cover rings but nothing in the wells. Should be OK.
 

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Thermostat should be a Mahle or from Subaru.
Spark plugs NGK
Don't change the water pump. Unless tap water has been used in the engine it should be okay.
Brake fluid is 2yr/20k miles
Diffs, depending on how the car is driven, 30-40k miles is good. You could pull the fill plug and check the color of the oil. If it's getting close to coffee color, you're overdue.
 

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Discussion Starter #9 (Edited)
I'll do the thermostat. Spark plugs are Subi OEM. Never used anything but DI water for cooling and over 10 years probably not more than a gallon was added (zero leaks). Coolant need to get from the dealer. I did the AT fluid 2 years ago (it costs both arms and legs here) but the brake fluid needs to go. The diff oil is nowhere near brown, I used Red Line (smells nasty). Castrol rules over here so I'll probably swicth to this. Diff oil caps = breaker bar, that's what I remember ... T70 socket IIRC ...
 

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I’ve heard of a few oem ecu updates that would also program for the idle to suddenly drop low on occasion. Have not found anything to substantiate this.
 

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Discussion Starter #11
Guys, it was the battery/comp indeed. I disconnected, re-filled with DI, recharged properly and reconnected - the idle dropped to 3-400 rpm almost dies every time. it was really bad. But I kept driving for a few days with no change. It gradually - slowly - improved over about 200-300 miles of mostly city driving. Mind you I have NOT recharged the battery anymore (I replaced the spark plugs but that made no change and it's a different story) just drove and drove. Now the car is back to normal. I guess the comp finally "learned" the battery behaviour.

And the off-topics. The spark plus were at about 60K (the car is at 105K miles) and were OK with buildup but there was a visible pit on each ground electrode, the distance was surely off spec. I found some oil in Cyl 1 plug well but the other 3 wells were dry and there was no sign of oil drying on the plugs body. I'll leave it like it is.

I cracked the 13mm square bit from Harbour Freight for the rear diff cap while using 45cm breaker bar and 1/2" to 3/8" Stanly drive adapter - not the cap and not the diff cover gave in :) Now I'm waiting on a Ko-ken japanese bit shipped from UK. If I crack that one too I'm talking the cover off :)

And before I get to the belt I can't find radiator upper hose. The local dealer - which is 50 miles away from the factory in Belgium - can't source it either. That's the way it work out of US I guess ... "so what do you do if you tear it when you have to take it from the flange" I asked the dealer 'We fix it" he calmly responded. Good luck with that.

I guess I have to get one from US and cover shipping and customs ... comes at about $70+ ... or get the Duct tape ready

Thanks and good luck!
 

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Discussion Starter #13
I wish I did. I did some WD40 and I guess at least 150lbs of force by pressing on 2' breaker bar with my leg - it finally gave in, at 8PM after 1+ hour of fight. The German breaker and the Japanese bit held great (no adapters) - its amazing how much force steel can take. **** tight - and that's considering I replaced that one like 6 years ago. Anyway, the funny part was the drain plug was far far less tight, it gave in almost immediately. Maybe there is smth about the fill plug.

As it was already dark I just put them back and will do the drain and refill today.
 
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