Can a coil cause a rough idle -small misfire, but not make a massive misfire that it will go undetected? I have no misfire codes, but my idle is rather erratic (slightly-nothing major), and i am just not happy with the performance......Plug connectors are new ....

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1993 300E, 2.8 M104 .....

its possible ... the reason I say this is I had a misfire issue (under load) when would try to pass someone. I had to check the codes a few times until the car finally had a misfire code present. I then moved the coil to another location and the misfire code followed that coil

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1994 E320, 145,000 miles

Make sure you have the exact correct plugs in it.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I have the correct FD8C plugs......

so if there is no misfire documented in the system, i should not worry about it and look for something else?

Thanks,

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1993 300E, 2.8 M104 .....

I suggest coil and coil wire. With over 200K original miles I was not the original owner I replaced the coils which were date stamped 1992.

not sure if you want to test your o2 sensor .... mine was bad even though that didn't make the check engine go on ... i had a rough idle that cleared up when i replaced the o2 sensor ... not sure if you are in the same boat as me, but my o2 sensor got fouled up from the misfire issue

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1994 E320, 145,000 miles

O2 Sensor is a good idea. Really helped my idle in my 300E and I used a '95 Mustang O2 sensor that I spliced in. Was pretty easy to do.