I have 2003 Outback, 95000 miles it sputters & backfires. After I shut it off for a few minutes it starts up and runs fine. It will run fine for hrs, days or weeks, then it does it again. No check engine light. Can any one help ?

Bad valves system.

Or

timing belt system.

check engine light on? any codes?

 

.

no check engine light & no codes.

have it scanned for pending codes.

 

maybe you have a sticking valve.

 

seems unlikely to be a TB issue since it's intermettent.

 

might be good to put a vacuum gauge on it and start moving pushing pulling on hoses and harness bundles. If you can make it stumble, then investigaet for cracked vacuum lines. If vacuum is steady and it stumbles, look for loose connectors, bad wires, etc.

 

has the car generally been well cared for? plugs and fluids changed per schedule, etc. ?

Could be bad spark in the chambers the origin of these problems could be:

 

Bad/worn spark plugs

Wrong brand spark plugs -> get NGK plugs

Worn spark leads/cables -> get original or NGK

 

Does it happen with wet or very moist engine bay (= cables)

 

Additionally could be broken inlet valve (backfire in top) or broken outlet valve (backfire in exhaust/catalytic unit).

 

I would check the plugs and cables first, if not do a compression check.

Could be bad spark in the chambers the origin of these problems could be:

 

Bad/worn spark plugs

Wrong brand spark plugs -> get NGK plugs

Worn spark leads/cables -> get original or NGK

 

Does it happen with wet or very moist engine bay (= cables)

 

Additionally could be broken inlet valve (backfire in top) or broken outlet valve (backfire in exhaust/catalytic unit).

 

I would check the plugs and cables first, if not do a compression check.

 

 

good point on the sparkplug cables.

 

You could try using a water spray/mist bottle under the hood at night. Spray the coil and plug cables and monitor for sparks, missing idle.

 

Subaru dealer is best for replacements. many reports of problems with other brand cables.

good point on the sparkplug cables.

 

My cables are still bad and cost about 50 dollar EACH!!! over here at the dealer. And from time to time (autumn when moist) I also have backfires, 2 to 3 cyl running but never had a CEL.