saving4one

My CEL came on Saturday afternoon on my second run at Freezeout Hill-climb, so I was in hot high-rev conditions for just under 2 min. Went to Auto Zone had the code read: P0301, had it cleared. Asked a tuner with a Subie team what he thought, so I borrowed some tools and checked #1 spark plug (maybe 10k miles on plugs, NGK PFR7G-11S) looked good, swapped coil #1 and #2. About 15 miles later CEL back on. Next morning back to Auto Zone: P0301, P0302, P0300, P1399. Had them cleared, had to go to O'Reillys for plugs (NGK IFR7G-11KS, not the same plugs but what their system brought up) changed all plugs in parking lot, put #1and #2 coils back in original position. CEL came on as soon as I started it, put code reader back on same bunch of codes, but I did not get a print out as I did at Auto Zone, random misfire, not just cylinder #1 as when first initially read. Cleared code, O'Reillys employee said it might have been ready to throw the code just before I shut it off to change plugs. Added Royal Purple injector cleaner, filled my tank at Chevron, drove from Emmett ID to Biggs OR ~300 miles, no CEL. Filled up in Biggs CEL came on at start up. Went to bed at Motor Inn at Biggs. Now it is morning, and here I am.....
I have owned my S since new, performed obsessive maintenance, never added injector cleaner, never had a CEL come on, 65500 miles currently. I did put a new battery in last year and have not done the idle learn procedure, laziness? Idle has been ~850 with a dip here and there since new battery but I just kept putting off idle learn procedure. Since yesterday after adding injector cleaner and cruising at 70mph on I84 cruise control would fluctuate up and down 1mph every 15 seconds or so regardless of load. Did not do before. Also at start after filling up last night car almost didn't turn over and idle dipped to just 1 thin bar of RPM but did not stall.
I am going to drive to the next O'Reillys in Madras about 2 hours away to get this new code read.
Any insight? Hopefully I am not doing any damage, other than idle variance car is running as normal, I did one more run on Saturday and luckily it didn't cut power or go into limp mode (ran good enough to set my best time up the hill).

King Tut

The one time I had issues with CELs and random misfires it turned out to be the fuel pump and not supplying the injectors with the correct fuel pressure primarily at idle.

saving4one

Thanks Tut, the tuner that I was talking with did ask where the fuel filter was. I'm not looking forward to dropping the tank! Is there a way to rule out the pump or filter? If it was a bad injector would the CEL be for that? I also forgot, I'm totally stock, no engine mods, just suspension.

windhund116

When is the last time you adjusted the valves?

saving4one

Last year? I've done that properly (totally cold engine, etc) at least 5 or 6 times in the life of the car. Last time there was very minimal adjustment, would this issue have shown up earlier than this if it was valve adjust?

windhund116

Then, I'd do a compression test to see if valves and rings are sealing ok.

Good luck!

King Tut

You don't have to drop the tank, haha. It's really easy if you don't have a soft top and your hard top is removed. The fuel filter is just a sock filter on the end of the fuel pump. Remember the issue is occurring in all cylinders which means you need to think of things that go to all cylinders.

Slowcrash_101

Probably coils, but could be fuel injectors. I'd check the fuel trims, and the o2/lambda voltage. You can hook up a cheap obd blue tooth scanner that hooks up to your phone and it will give you live readouts for that.

saving4one

I just arrived home. I stopped in Madras and now #4 had been added to the misfire list. I cleared the light and it has yet to come back on. I filled up with non ethanol 92 and another bottle of cleaner in OR just before the CA border. I was expecting the light to come back on every time I would push the start button.

Tut, did you think my symptoms sounded like the fuel filter or fuel pump? Unfortunately my soft top is not removed, I need to familiarize myself on fuel filter/pump removal in the Helms manual.

Slowcrash, my neighbor has a scanner that does live readouts, I think. I guess it's time to find out.

windhund116

Why not do a compression test first? You need to rule-out improper valve and ring sealing first. Before you try hit-&-miss replacing parts --- then, come to find the engine has burnt valves or weak sealing rings.

At least, that is what I would do.