Error code PO300

I need help soon please. Have a 1997 Sufire with 148,620 miles on a 2.2L 5 speed. Check engin light came on error code PO300 multipal engin missfires. Chaned plugs used a HIV spark tester had what looked like good spark on all cyclinders. Checked wires for Obvious cracks or shorts found none. Car starts fine half a crank she is runningseems to do fine at lower rpm's but soon as it hits 4,000 rpm if just quits like someone turned it off. From what I resheared on the net a error code like that don't nesserely mean a ignition. Fuel pump, other bade sensor like rpm or high rev. Thnx any advise would be fine.

I had the same problem with my 1997 Sunfire. Check all the electrical connections on the engine, especially the throttle body. The Multiple/Random Cylinder Misfire code your receiving could also be a bad ground connection. Did you recent power wash the engine?? If so a hair dryer or hot air gun can usually dry the areas that retain water. I found both the AIC solenoid connection to be a factor as well as excessive water inside the conduit covering the wire runs. Hope this helps.

I took mine in for diag. they#3 cylinder dead. Then because of it it jumped time. Mine was doing same as yours, coming up PO300.
Looking for an engine or to sell it. If you know anyone, $1200 firm. Just bought car. New paint job and interior is great. Having all the recalls done on it when I had the diagnostics checked.....I was (am so bummed)