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1990 Legacy -- jumping idle


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16 replies to this topic

#1 92_rugby_subie

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Posted 23 September 2012 - 04:15 PM

When starting the car when cold the idle surges... goes up to about 1200rpms, down to about nothing, back up and repeats a few times.... have to pump the gas and keep the idle up for about 5-10 seconds (depending on outside temperature) to keep the car from surging idle. So far it hasnt died... just makes it really hard to drive without letting it sit awhile.

It also does this after not running for a few hours... Say during a work shift... but its not as bad as first thing in the morning.

Coolant temp sensor replaced (from Subaru)
Unplugging the intake sensor shuts the engine off so Im sure thats functioning correctly.
O2 sensor needs replacing (getting horrible gas mileage) which will be replaced this week or next week (was told Bosch universals are okay? or should I just go with Denso?)

Anything else I need to check? Thinking if I cant figure it out Ill take it to GD and have him scrutinize the engine reseal that I did.

#2 WoodsWagon

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Posted 23 September 2012 - 05:14 PM

Try cleaning out the idle air control valve with carb cleaner. It's the thing bolted to the side of the intake next to the throttle body that the 1" rubber hose goes to from the intake tube.

#3 GeneralDisorder

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Posted 23 September 2012 - 07:02 PM

The '90 manual trans IAC's were junk. You can try to find a used match but it will most likely be just as bad if you can find one at all. Only good fix for these is to update the computer and the IAC to a '92 - '94 units. Along with the injectors as those were also troublesome.... or perhaps buy a new IAC from the dealer but that will probably be more than the car is worth.

GD

#4 92_rugby_subie

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Posted 23 September 2012 - 11:11 PM

How hard would be upgrading that all be? and would it even be worth it in the end?

The car in all honesty is only temporary... Next year will be a 91-94 wagon, 5 speed, AWD and be getting a frankenmotor and all the nice stuff....

#5 mikaleda

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Posted 25 September 2012 - 11:02 AM

Personally I wouldn't use one of those universal oxygen sensors. I tried that once and it didn't work at all.

#6 Fairtax4me

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Posted 25 September 2012 - 11:59 AM

Universals work fine if you get them hooked up correctly. But Rockauto has exact fit Denso for like $50. They also list an NTK sensor for $38 but doesn't say if it's exact fit or universal. NTK is a sister brand or NGK, so their stuff will certainly work in a scubaru.

#7 92_rugby_subie

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Posted 25 September 2012 - 04:58 PM

I guess Ill have to ask them :P

Cuz I found a denso on ebay for like 55 I think... and a universal for 12....

But 38 would be good if it was a direct fit :)

#8 92_rugby_subie

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Posted 25 September 2012 - 05:02 PM

http://www.amazon.co...=au_pf_dp_chart

Part number 24614 for the NTK seems to be a good O2 sensor for Subarus... :)

#9 eulogious

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Posted 01 October 2012 - 07:45 PM

The '90 manual trans IAC's were junk. You can try to find a used match but it will most likely be just as bad if you can find one at all. Only good fix for these is to update the computer and the IAC to a '92 - '94 units. Along with the injectors as those were also troublesome.... or perhaps buy a new IAC from the dealer but that will probably be more than the car is worth.

GD


Upgrade the IAC? I didn't know that. I should do that. I just upgrade all my injectors to redtop and upgrade the ecu as well. Just updating the ecu was a big difference in the way my car idled. I had the same thing about in my legacy (auto though, not manual), and upgrading the ecu and the injectors solved that issue for me. Much better now.

#10 92_rugby_subie

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Posted 02 October 2012 - 01:04 AM

Are the ECU's plug and play? Im not really looking forward to tearing into the car more... Except its leaking coolant onto the lower radiator hose... from either the overflow bottle or the radiator, havent checked into it really.

#11 eulogious

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Posted 02 October 2012 - 02:09 AM

Yup the ECU just plugs right in. Gotta move some stuff around to get to the ECU but the '92-94 ECU plugs right in. The injectors are super easy, just swap the whole fuel rail. Took about 20 min to do! Nice upgrade for sure. It kicks up the idle when you start it like all newer cars do, much better than the stupid '90 ECU.

#12 ivans imports

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Posted 02 October 2012 - 10:21 AM

i see this problem when is low on coolant the temp senser gets above the coolant level and dosent read properly check coolant level or icv or somone has addjusted the tb hard stop

#13 92_rugby_subie

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Posted 03 October 2012 - 01:41 AM

So car is a 5 speed FWD... Do I need a 1992-1994 ECU from a 5 speed FWD or can it be an auto/manual and FWD/AWD?

#14 92_rugby_subie

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Posted 06 October 2012 - 03:05 AM

Bump.

#15 GeneralDisorder

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Posted 06 October 2012 - 01:21 PM

You need a manual ECU. They don't care about AWD/2WD.

GD

#16 92_rugby_subie

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Posted 06 October 2012 - 01:52 PM

Thank you Rick!

#17 ivans imports

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Posted 11 October 2012 - 10:35 AM

have two 90-91 legacys right now that loose pulse on injector 1 at idle but ok when reved up narrowed it down to worn out idle motor




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