Any updates on this ???
I have same problem on my 4 cyl 96 mystique.
Idle is at 1100 rpms, then 1 second later, goes down to 800, and it keeps doing this ... Up and down, up and down, very regular pattern. Sometime it will die on me at a stop light.
Runs much smoother if I turn the AC on. Idles at 1000-1100 rpms and it pretty smooth.
No CEL.
I suspect a vacuum leak at the PCV but not too sure. I might look this week-end.
Could a misadjusted TPS do that ?
Any ideas.
iougs-
