Large Spark Plug, Engine Pinging

[BusyDad]

Hello I have a '97 DOHC. 90,000 miles. Bought it @ 84,000 miles. Noticed light pinging, Service Light came on once up a hill, went away later that day. The #2 spark plug is larger than the others, same heat number however. Had a Service Light msg. come on during fwy. driving one day at 63 MPH. Took in to a shop, asked to please diagnose that, and find solution to enging pinging. Asked them to check plugs.

Shop replaced coil pack, said they found error messages indicating #1 and #3 cylinders misfiring (again, #2 plug is the large one) Plug wires were replaced 3,000 miles ago, air filter in good shape. Oil changed every 3,000. Had fuel injectors cleaned. New PCV valve. At emissions check, .50 is allowable Hydrocarbons. Tested 0.48 (July '03)

After getting coil pack replaced, car still pinged. Then, a rough idle started. Service light came back on. Took to Dodge dealer for diagnosis, said #4 cylinder showing 60 on compression! Could not read #2 cylinder.

Ideas? Am going to put old coil pack back on to see if idling smooths. Idle is rough only at stop, it is fine at 1,500 RPM.

EGR? O2 sensors? Cam sensor? New head? May as well get a rebuild if it needs a new head. Codes never showed error for #2, car has lots of power besides the rough idle at start, don't like the pinging.. and now the service light. Thank you in advance!

[blachdohcneon]

first off what octane gas are you running? the dohc needs 89 or better or it will ping.

stripped #2 cylinder so they tapped it a larger size?

as far as cheack engine light, when thats on turn key on-off-on-off-on then it will blink a certain # of times indicating the code. The codes can be found on neons.org