Sporadic rough idle.....

This has stumped me and my mechanic buddy.....

My 2003 3.4 TRD PreRunner has developed a sporadic rough idle that varies in intensity. It goes away when driving and get to about 1500 rpm. It becomes much less severe when stopped once being driven for a while.

The "roughness" of the idle is not consistent but more random "chugs" or "misses". They can be close together, far apart or completely sporadic. Sometimes barely at all. Always present at first start of the day and subsequent starts and at rest, worse when the humidity is high though.

**It is very very bad when the humidity is high**. During rain or foggy, damp weather, it is very present and intense. It has been getting to -5 C lately and temperature has had far less impact on the severity or frequency of the roughness as high humidity has. The idle is very noticeable when accelerating for the first time in the morning on a high humidity day and must be driven for a while before it calms down at a red light.

It never stalls out or loses power when driving.

There is a small exhaust leak, just before the muffler I think.