I've had a rough idle problem for months and I'm at a loss as to what do about it. Here's the specifics...

- It idles rough only when less than 500 RPMs. It gets rougher when it's cold and/or damp outside. Everything else is great!
- I have had the following replaced in the last few months: Engine wiring harness, throttle body, distributor caps and rotors, spark plugs, spark plug wires, engine mounts. None of these had an impact.
- An engine compression check shows compression as good as new. There are no codes being stored.
- The car only has 67K miles on it.

The problem seemed to start after having my enginer steam cleaned, but I also had the engine mounts replaced right after, so it's possible it started before.

Any ideas?