Pontiac Repair: 1999 sunfire running rough, chevron techron fuel system, chevron techron fuel system cleaner

Question
I bought my son a 1999 Sunfire that had been sitting a year (old gas). It starts and runs fine when cold, very peppy but sometimes feels like it is running on 3 cylinders when hot, firing erratically and under powered. I cleaned the coil pack connections (which were rusty),  changed the oil and plugs and added injector cleaner. The check engine light is on and when the car was etested of course it started running on 3 cylinders during the idle test and failed (passed the other test). I am wondering where the problem might be and what to change next.

Answer
Hi John:

well first off I would replace the spark plug wires if the tops of the coils are rusted that means they were more then lilkley arching in the wires. Use only AC Delco wires or good quality wires from a good parts store like a NAPA or Carquest if there are around up there in CA. Also it's a good idea to replce the spark plugs just as rutine maintence. again Use ONLY AC delco plugs.. Next I would get a bottle of Chevron Techron fuel system cleaner and add that to the tank and fill the tank up with fresh gas and run  that tank through and see how it runs.. It's either a spark issue or an injector that's plugged/lean I'm sure.. More of a spark issue then anything else. You can spray the engine down with a spray bottle of water and if you have a spark plug wire that is leaking it will show up and the engine will start to misfire to confirm the wires are bad... Yoummay need to load up the engine while trying this by putting the car in drive step on the brake pedal and run the engine idle up a bit and if the wires are leaking with water sprayed on them the wngine will misfire just like it does going down the road. Just be careful you don't take your foot off the brake and hit anything. You may want to set the parking brake as well when you try this.