Engine runs rough for few miles

[Startiger]

Yesterday, when I started by OB up from being idels for the weekend, it ran very roughly. With the car in reverse and not moving, the whole car shook. Once I was out of the driveway and moving forward, the car had a noticeable lack of power, very hard shifting.

When I was accelerating, the car again shook, low power and shifted hard. I noticed that when the car was shaking, the check engine light was flashing. But when coasting, the car settled down and the CEL with off. Go to accelerate again, it shakes again and the CEL flashes.

It did this for about 2 miles before it started behaving normally. The rest of the day it ran okay.

I am planning to get the code history read tonight, so I'll post back on what codes it stored.

Ideas? Bad plug/wire? Bad gas? Water in the gas?

Got about 48,7000 miles on it at the moment.

[plain OM]

Was it wet and cold over the weekend? If so, I had the same experience. See: Coil failure common in MY2005-9?

Bad spark plug wires, coil housing, or water in the fuel are all possibilities, but if it was both wet and cold, I'd lean toward the first two.

I wouldn't be surprised if the codes are misfires.

See also: http://www.subaruoutback.org/forums/...odes-dtcs.html

[Startiger]

It had been a cold weekend, but that morning was warmer than it had been. It was damp.

I replaced the plugs at ~30,000 miles, but it is still running on the stock wires.

[plain OM]

Faulty wires or coil can be the cause, but finding out which (if either) is more difficult.

Some here suggest idling the car in the dark and misting water (very fine spray) around the coil and spark plug wires. If there's a high voltage leak, the moisture will "draw it out" and either there will be visible arcing or the engine will falter. I'm not sure this can always be decisive, but it's something worth considering.

[Startiger]

Got the code read last night, it's a P0303, cylinder 3 misfire. Autozone guys are saying bad wire or plug, but sure if I trust them.

Replacing the wires and plugs is easy enough and a reasonable price. However, $206 for the ignition coil is a bit steep for me at the moment. If it is the coil, would that be covered under the 60,000 mi powertrain warranty?

[ron917]

My '07 Outback was doing the same thing on very damp mornings with heavy dew. When I looked under the hood, condensation was literally dripping off of everything. The wires sparkled in the sun like spider webs.

My ignition wires were very dirty form dust and crud. Pure water is an insulator, but water mixed with other stuff conducts pretty well depending on what that other stuff is.

Since I'm cheap, I figured I would try cleaning the ignition wires before buying new ones. I pulled them out and wiped them off with water and dish detergent. I let them dry and coated them with silicone lube spray before reinstalling.

So far, the problem has not returned on similar very damp morning with heavy dew.

It probably wouldn't hurt to also clean the coil housing.

[plain OM]

ron917

Cleaning the wires might be a good way to help locate the cause of the misfires but, it seems to me that, if the dirt+moisture mixture on the wires is providing a conductive path for the high voltage leading to the misfires (which is very possible), then the wires are faulty. The high voltage should not be getting out to the surface of the wires to begin with.

[Jahallah]

Same code, same conditions, more mileage.

I ran into this first about 2 years ago, my 07 ob had about 70k.

Rough idle and severely reduced power after cold damp starts. It always went away after a few miles. Code read was cylinder 3 misfire.

This went on for two years, maybe 10 times total.

I researched here and found the same causes. I was determined to find the cause last spring and even tried the misting technique. Could not get the problem to reproduce. never replaced anything, lost my job so it never got fixed.

I replaced the spark plugs a few months ago, end of summer. And throughout fall (NE weather) i haven't had the problem occur once. Fall and spring are when the problem occurred the most and I'm guessing it was an arching plug.

I will update you if this changes.

$18 fix