Chrysler Repair: Rough Idle 2,0L HO, champion spark plugs, vacuum hoses

Question
2002 Dodge Neon R/T
2.0L HO engine
5 speed

Hello, just in the past week all of a sudden I was driving down the highway and the check engine light came on.  I stopped at autozone real quick the theyre scan tool said it was a "#1 cylinder misfire".  At the time I couldnt feel any significant change in idle.  So I bought champion spark plugs, and OEM plug wires from the dealer.  Also used a can of seafom in the brake booster line and fuel tank. Now it seems to be running very poorly at idle!  I can feel it shake and see the engine too.  Checked for spark from coil pack w/spark tester tool, and got spark.  When I pressed down on the engine a person in my car said it felt better.  But the CEL is still on.  Any help would be wonderful because of course, this happened the week I called the autotrader to sell this car!

Answer
Hi John,
You might do well to get the codes read again because the engine is performing differently than when it was first read. The "pressing down" observation would possibly suggest that the intake manifold may be leaking so a check around that structure for loose fasteners and disconnected vacuum hoses would be a good thing to do. I am unfamiliar with seafoam and what its purpose is in the vacuum line for the brake booster. Do you attribute the deterioration to that product?
There are at about 18 different possible reasons for multiple cylinder misfiring so it is difficult to suggest which one(s) is the the most likely to be the reason. If the problem seems to be most noticeable at idle, then you might want to check the egr valve's stem to make sure that it is moving freely and if not the spray some lubricant on the point where the stem enter the body of the valve and lever it open and closed with the tip of a screwdriver placed in the stem's slot. Aside from that, having a shop check the ignition system with a scope and also attaching a vacuum gauge to the intake manifold to look for charcteristic malfunctional behavior would be worth trying.
Those are some ideas to consider.
Roland