idle problems

working on a 93, 4.0 automatic with 267,000 miles...

when idling it will sometimes (random and not often) slowly drop idle speed, kinda make some knocking sounds before the engine picks up speed again ( up and over 1,000RPM) then it settles back down to idle speed.

seems to do this more when cold than warm.

does this in any gear (including park and neutral) so i am thinking more of TPS or IAC rather than a torque converter or trans problem.
your thoughts?

Timing chain

drives great though, seems to be that it goes away after the throttle has changed position (via the gas pedal)

can you explain why it might be the timing chain? it goes down the road great.

My guess would be on the IAS,...getting stuck. Try removing and cleaning it, both the the pintle and inside the throttle body.

took out the IAC and cleaned it up, no change.
where else can i look.
it really bogs down, sounds like its knocking and then will pick back up speed like when you first start it up (1500 RPM or so) and then work its way back down to idle.

any ideas?

Got an oxygen sensor, I think that has solved it
http://www.naxja.net/forum/showthread.php?t=1096894