I had a similar problem that felt like slight missing and the idle would vary once in awhile (also very slightly). Tried new spark plugs, it ran like new...for a few days. Then it started over again, a little different but I could tell it wasn't 100%. I started thinking about spark plug wires, etc. Tried injector cleaner thinking it was a fuel problem. Never got a check engine light and no codes were stored when I did the stomp test. Could hear a different note from the exhaust, sounded deeper, performance wasn't smooth as silk all the time, as it should be. Finally put 6 new coils in, OK for a few days. This has been over a period of the last year since I bought the car. Most of the time it was fine, then it would run funky for a bit, it was driving me NUTS!!! Finally, somebody asked if I used Di-electric(?) grease on the connectors. Well, uh no, I didn't. Went to Pep boys last Saturday and sprung for a tube, a big $3.00!! Took the coils and connectors off and put a dab in each end of the connector.
What a difference. Idle steady and smooth, performance A-1. Now I can REALLY feel the difference that the EAT chip makes. Makes me wonder if my coils weren't bad to begin with but with 130,000 miles, I figured they could stand to be replaced anyway.
I had never heard this grease mentioned by anyone before, or I was not paying attention when they did. A BIG difference for a little bit of time and money. Try it before you spend money on anything else.
If your connectors are real dry or cracked, they can be replaced separately, they are available from BMA for $5.26 each. I didn't replace mine with the coils but they looked fine.
Good luck!
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