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We have a 99 Legacy wagon with the 2.2 motor.  It has recently started missing some when cold.  Now, it's not really cold yet....so we're talking about the 60's here, not below freezing.  When you drive the car maybe 3 miles, it goes away and runs fine.  It doesn't miss or hesitate later in the day either, even if it sat all day. 

 

I had similar problem a while back and that time it was the Idle Air Control, so I took this one off (which is very easy on a 99 compared to a 95) and I cleaned it with carb cleaner to get all the carbon off the moving vane. 

 

It still has the problem. 

 

I'd really be interested in help from someone who had the exact problem, so I can avoid rabbit trails.

 

Thanks for any suggestions!

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bad sparkplug wires, maybe coil,  can do this - sitting overnight allows a little condensation to form, causes missing until engine heat dries the high voltage parts out.

 

OEM wires are the only ones with no complaints, other aftermarket brands often won't work well for people.

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bad sparkplug wires, maybe coil,  can do this - sitting overnight allows a little condensation to form, causes missing until engine heat dries the high voltage parts out.

 

OEM wires are the only ones with no complaints, other aftermarket brands often won't work well for people.

Agree, needs new spark plug wires. Buy a good set, cheapie wires don't hold up and last very long in a Subie. Also, change spark plugs can also help. Perhaps the cold start sensor needs to be replaced. However, I think if it is going bad it sets off a check engine light.

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Coolant temperature sensor.

Use a scanner to check cold engine temp..

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Thanks for the comments so far, guys.  I will check into those things this weekend if possible. 

 

The car does have new plugs.  I put them in earlier this year.

 

I know that these cars operate on some kind of pre-programmed basis until they get warm.  Could the coolant temp sensor affect that?

Once in the past with another Subaru the local Subaru experts recommended one for a similar problem, and it didn't make any difference.

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You would have to scan and watch live data.. If its not reading cold enough it could be doing that. Ecu always uses coolant temp.

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while the car is idling normally at night with the hood up, you could spray the spark plug wires with a plant mister of water. Watch for the engine to miss and maybe see some arcing on the coil or wires. New plug wires would not be an unusual swap on any 17year old car. OEM wires only, many folks report issues with other brands.

Edited by 1 Lucky Texan
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CTS can fail in ways that mess up drivability without causing a code. There should be a chart in the FSM that shows temperatures vs ohms. If it's not steady, and in spec, it's bad.

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What kind of plugs?

Did you replace the wires? If so what brand of wires?

 

I know people here will scream, but I put in double platinum autolite plugs.  The reason for that is that I have a Windstar Van that came with them from the factory.  A couple years ago I had to replace a coil, so I decided to change the plugs also.  I was astounded to see that with over 100,000 miles on them they were still good!  The gap had not opened up, they were not eroded...nothing bad.  So I was so impressed that I started buying them for all my cars. 

 

I did not change the wires. 

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I did not work on the car over the weekend because it was extremely windy here on Saturday, and I was busy also.  Today I plugged my code reader in to read the temp readings on my drive to work.  The temps seemed pretty normal.  The car had run a minute before the reader got plugged in and was reading the info.  The coolant temp was 100 and slowly rose to 190 as I drove.  (Like I said, the car had run a minute or so) 

 

The car ran fine this morning.  So this also is puzzling.

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Double platinum should be fine. Autolite isn't a brand I normally recommend, but I don't think those are the problem.

Wires on these need to be a good quality brand and they should be replaced whenever you replace the plugs. Double check that all of the wires are clicked on all the way. Also check for any moisture in the spark plug wells. I've had to resort to RTV on the plug boots to keep water out of the plug wells because it will cause misfiring until the engine warms up.

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Double platinum should be fine. Autolite isn't a brand I normally recommend, but I don't think those are the problem.

Wires on these need to be a good quality brand and they should be replaced whenever you replace the plugs. Double check that all of the wires are clicked on all the way. Also check for any moisture in the spark plug wells. I've had to resort to RTV on the plug boots to keep water out of the plug wells because it will cause misfiring until the engine warms up.

I still have the wires on the car that were on it when I got the car.  I think they are original, but I need to check. 

 

I did have a guy do alignment on the car a few weeks ago, and I should check to see if he loosened any wires or bumped anything under there. 

 

Yesterday I drove the car with the code reader on from absolutely cold, and the temps all read the air temp to start and the water temp increased in a way that looks accurate to me.  It didn't seem to hesitate yesterday either.  I'm wondering if my daughter bought some bad gas.

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Probably one of the most common problems that causes misfires is plugs and wires.

 

I've never seen a coolant temp sensor fail on a subaru, not saying it can't happen but its very unlikely.

Edited by mikaleda
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I cleaned the PCV and replaced the front O2 sensor over the weekend.  It didn't help.

 

I was passing the Euro Garage in Leola today, and saw them cleaning it out.  Apparently they moved out.  I was looking for possible Subaru parts, and got into a conversation with a mechanic who was there.  He felt that the spark coil was a possible culprit.  This was mentioned by 1 Lucky Texan earlier.  I think I'm going to look into that next.  My Windstar was having a similar problem a while back, and it turned out that the coil was cracked underneath.  So maybe something similar is happening here.

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OK I think it's fixed.

I bought a original Diamond Subaru coil and a set of wires on Ebay.  The seller did not know the brand of the wires, but the ad claimed that the parts had 200 miles on them.

 

I started with the coil first.  It made no difference.

I did the wires on the passenger side next, since that's where the code reader found a misfire one day, and had to do it quick before work.  That seemed to fix it.  So I put the "new" wires on the other side the next day, and it DOES seem to be fixed.

 

Thanks to 1 Lucky Texan, Rooster2, Fairtax4me, and mikaleda for all repeating about the wires.  Thanks to everyone who took the time to comment on my question.  I appreciate all of the comments.

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Just an afterthought to pass along:

 

I was a bit hesitant to suspect the wires because my experience with wires goes back to my 66 MGB.  Back then the wires were so bad that they cracked after they got old.  You could literally see sparks come off the wires all over the place at night. 

 

Today's wires are incredibly good compared to that.  I have never seen a cracked wire on my current cars.  BUT...I suspect that what's going on with bad wires is some sort of break or vibration problem where they crimp the metal spring ring onto the core of the wire.  Maybe that's not it...but that's a theory I speculated about today. 

 

The bottom line is that they can LOOK good, but that doesn't mean that they ARE good.

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