Forester Engine lights

Asked by Guru17QVQ Sep 30, 2019 at 03:44 PM about the 2006 Subaru Forester

Question type: Maintenance & Repair

My 2006 Forester (my baby!) started shuddering at
idle and take off about a week ago. Yesterday I
cleaned the intake sensor, battery connector,
changed the engine filter, and added seafoam.
Yesterday and last night it did not shudder.
Today the check engine light came on, and about
five minutes later the cruise control light started
flashing. Auto zone said Code was P0303.
I bought new spark plugs, wires, and coil.
Wondering if anyone else has dealt with this, or
anything else I should be thinking of?

2 Answers

271,245

I think you are on the right track. Install the parts and see if the problem clears up.

1,040

Oh brother! Stop throwing money at it! PO303 simply indicates a misfire at cyl #3 (rear, right side). First check its spark plug for a missing anode (famous on the plats), gobs of oil from a cracked spark plug seal in the valve cover, or loose wire insufficiently pushed onto the plug. If all ok, redrape the #3 wire AWAY from exposed metal at least a half inch. If the wire was clipped in adjacent metalware look for a tiny white spot on the cable, indicating high voltage shortage to ground (hence the misfire). Replace that wire if compromised. Check for corrosion where it seats into the coilpack too, as those brass contacts can rot away. Then test at idle and upon acceleration if there's still stumbling repeat a few times in order to get a code to set up. If still 303 only you may have a valve problem in the head, which I'm not sure I'd chase unless this 13yr old is otherwise pristine. But before giving up change the coilpack and all 4 ignition wires, since you've already bought them anyway. Again, be careful to NOT dress the new wires too closely to metalware; those silly plastic "dresser" clips are more problem than not. Floppy wires out in space are NO problem. If dealing with the ignition doesn't solve this try switching injectors on the left head. If the problem travels to the mate then pop in a new injector. Backing up, the shuddering from misfire is very much correlated with dampness. Following rainstorms I'd often found a real lightning show in the dark when watching raw Subies idle in my shop before repairs. You'll also generally hear a "tick" with each 1/4" or so arc of spark to ground. That may be the case if a coilpack tower is cracked, too, but usually they short internally with old age. I like NGK silicone wires, but they're often cloned. A bottle of strong fuel detergent isn't a bad idea, too, as well NEVER letting fuel level getting below 1/4 tank hereon. Good luck. These are usually resolved easily, unless you've a bad valve in the head.

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