Hope all is well. Maybe someone could help . I have a 2007 2.5 SOHC . I have a p0304 code . The vehicle has a rough idle . The flashing check engine light goes off as I accelarate and the car drives completely fine . There is the typical external HG leak which I had for 50k + thousand miles . The oil is clean ,car does not overheat, starts fine,runs well with no smoke or bucking . So far I : 

swapped spark plugs , swapped coils , swapped wires, changed the injector, cleaned egr , sprayed to check for vacuum leaks , cleaned PCV lines . Changed pre cat o2 denso with original equipment denso . Spark plugs are clean . This has me completely stumped. 

 

when I pulled the p0304 the LT fuel trim was -15 which prompted me to change the injector. Since changing the injector the car does run better I admit at idle . Any HELP  is greatly appreciated. 

 

car has 215k . And has been well maintained. 

probably the missing is causing some fuel to be pulled so, the missing is the first priority.

 

when you changed the wires and plugs (OEM went back on I hope?) was there any oil on the plug or plug boots? leaking valve cover gaskets can cause misfires.

Many thanks . I did not go with OE  but will try that . I did switch around the wires ,and that did not help . I did notice an exhaust leak in the rear by the Y that leads to the mufflers? It's a puff puff sound dont know if that could be the cause ? 

for plug wires - OE or NGK only.

parts store aftermarket wires are known to cause problems

Burnt exhaust valve. You should have addressed the head gasket leak 50k miles ago and done the valve adjustment at the same time. Now you need to replace one or more exhaust valves. 

GD

10 hours ago, GeneralDisorder said:

Burnt exhaust valve.

 

very possible.

Confirm by doing a compression and/or leakdown.

A burnt valve will show immediately.

There is a tendency in today's computer controlled world to forget about physical problems and the use of old fashion Mechanical testing to determine.

Many thanks . I'm going to do a compression test . I will let you know the outcome. Thank you so much .

Well . I must say after going to autozone and exchanging the initial wire set I sprung for the NGK Wire set part number 55004. I now have no more flashing CEL light on initial acceleration and the idle seems smoother . The autozone wires were 7mm and the NGK 8mm. I cannot get over all the time trying to chase down this p0304 code for a wire issue. I even switched the 2&4 wire with the old set and still had a code ? . Maybe the non NGK wires cant take the heat because it just turned summer . Any explanation is greatly appreciated. 

Thank YOU to all I sincerely appreciate it . Just really bummed at myself for not getting NGK

and lesson learned

 

That seems very odd considering you swapped wires from a working cylinder. I would be performing a compression test anyway. 

GD

Well I guess I spoke to soon . I reset the CEL all was fine went to fill up and light came on ugg. Not stalling and driving fine .I will do a compression test . My buddy who is a mechanic said since the EGR is on the runner that that might be an issue . Unreal. I am getting 26mpg btw no poping or backfiring . 

 

EGR is not the issue. It is not on a specific runner. Internally the EGR passage comes up as a stand pipe in the center of the plenum. Obviously the EGR gasses must be distributed evenly to all cylinders. Your buddy the mechanic clearly doesn't understand how this functions. 

#4 cylinder is about 70% of the burned valves we see. The other 25% is cylinder #2, with 5% being either #1 or #3. 

GD

Edited June 10, 20196 yr by GeneralDisorder

I remember reading a multiple page thread on another forum about a misfire (#4) that the guy changed every part in the car.  Car had the head gaskets changed previously by some shop so the shop was reluctant to take the heads off.  Eventually they did take the heads of and found a burnt #4 exhaust valve.  Definitely something to remember if you get a misfire that isn't solved with NGK/OEM wires, NGK Plugs and an OEM coil.

Wanted to wait until I replied to make sure the car was running with no issues. PROBLEM  ended up being a coolent tempature sensor . No codes ...nothing . Seems the radiator sealant or coolent conditioner left a film of glue on the sensor . Never experienced this ever . Removed sensor cleaned it and all is fine . I could not believe a coolent sensor could wreck havoc on throwing a misfire code . Unreal . Some might overlook this when no codes are present. Just my 2 cents . Thank you for all your help . Any explanation on how these sensors operate specifically relating to Subarus is appreciated. 

weird - what is the history of coolant additives? was it Subaru Coolant Conditioner?

No . I used blue devil some time ago it worked for sure but must of left a film (glue like ) on the outside of the copper. 

obtw - nitrous, you should get a moderator to change your user name from e mail , some unscrupulous types might harvest it for spamming purposes.