I received my annual P300 error a few weeks ago after a few days of engine stuttering. Sadly a p303 so I performed the surgery removing the manifold etc. All plugs were fine with some wear and typical orange tint. Replaced the coil. The car ran well for two hours on the highway and then began with mild misfiring progressively getting worse. I scanned the system again and found the same error! p303 I can't bear doing the job again. The misfiring starts as soon as there's an incline. If I take the engine out of overdrive it runs great.
I've put new gas in the engine and wonder if there is an air intake issue why wouldn't other cylinders be triggering the error code.
There doesn't seem to be a distributor for this engine otherwise I'd surely be changing the cap and rotor.
Any ideas?