Runs rough in cycles

[Jiinx]

Hi all.
I've got a 90 2+2 na. The car runs properly when it is cold and when it is initially warmed up. After about 15-20 minutes it starts to sputter at cruising to very low throttle. This goes on for a few minutes and then disappears for a little while (3-5minutes) then it returns. This cycle basically continues until I reach my destination. Any kind of heavier throttle acceleration the engine comes to life, with no signs of a problem, until I go back down and cruise. Best way to describe the sound is like a coffee maker percolating.
Any Ideas ?

P.S. Not getting any codes, and the oxygen sensors are functioning correctly ( according to the cars OBD )

[evildky]

when it starts to act up, does ti still ahve a steady idle? ideling on all 6 cylinders?

[Jiinx]

Actually it does. It's amazingly smooth. I thought it might be heat soak, but it was cool coming home tonight and it still did it.

[The Silent Genius]

i've had problems like this and they always ended up being either corroded electrical connectors (injectors / IAA) or vacuum/boost leaks.

[evildky]

does ti only act up once warm? once it starts acting up does the idle quality remain good?

[Jiinx]

only does that when it's been warmed up for about 20 or more minutes
Idle quality is almost flawless, acceleration is still great, it only has the intermittent problem when it is at cruising throttle or at light acceleration.

I will check connections and regrease them.