What are your RPM at idle once warm up?
When you say rough idle, do you mean it shakes the engine or RPM goes up and down.

There could be numorous reasons for rough idle at warm up, coolant temp. sensor, Oxygen sensor, distributor rotor & cap to name few.
I will start with good cleaning the ICV, it is known to cause all kind of issues with idle.
What is the history of the car, how many miles? regularly maintained ?
Did you tried "Fuel injection cleaner" of any kind, that might help.

Hope it helps

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

Rough idle - the RPM's are constant, engine basically shakes. RPM's are around 750-800. It's got 93k miles, and has always been maintained by a competent mechanic. Have used fuel system cleaners, but no impact on performance.

The RPM are correct and if they do not flactuate up and down, it seems like you do not have rough idle problem rather have an engine shake at low RPM. If your motor mounts are not bad, check your engine shocks, Front flex disc, Tranny mount, and finally differential mounts. All of these effect the engine shake at idle.

Keep us posted.
Thanks

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)