Has always ran quite before, starts right up, decent gas milage, no smoke, no burning oil. I was hoping to find a new (used) car, and sell the Maxima, before I had to renew the tags. Didn't happen. Inspection+Emissions and tag renewal were due at end of July. Last day of July I change oil and bought new plugs. Running out of time I get the oil done but skip the plugs, figured I'd take my chances. Emissions checked fine, no problems. 2nd week of August, find my new (used) car. Start driving new car, decide to give Maxima a complete wash & wax, inside & out, and put the new plugs in, getting it ready for sale. I did not drive the car since the new plugs, car just sat. Last week I finally decide to put finishing touches on it, getting ready to sell. I start it up, no problems, but loud knocking coming from engine. Thought it go away in a min after oil got circulated, but it didn't. Drove it around the block, knock got faster & louder with torque & RPM.
It sounds like a piston is hitting a spark plug. Did the old broomstick to the ear yesterday and knocking is coming from middle cylinder, rear side. Took out and checked all plugs on rear side, nothing unusual but middle plug was colored purple on the tip. Could this be from stuck exhaust valve? I'm going to pull off the valve cover tomorrow for a look.
Any advice?
Sorry so long.
-RT