power loss in phases, 89n MPV 6 cyl auto trans
 

I have a 89 Mazda MPV 6 cyl with automatic trans. It idles nice, accelerates nice, but when it gets going on a nice steady roll about 40 mph it starts losing power in a rocking manner, sort of like a rocking chair. I rock forward 3 seconds with acceleration, then fall back 1 second with deceleration. I doubt its a slipping tranny because I would hear the RPM surge while it was slipping. I changed the fuel filter, put new plugs on, checked the EGR valve. My engine problem light is on too, and I tried to ground the green plug and turn on the ignition to get the code, but the code didn't show up, no blinks. Any help would be greatly appreciated.
thanks

RE: power loss in phases, 89n MPV 6 cyl auto trans
 

well, I changed all the transmission fluid today, even flushed out old fluid by shooting it from radiator directly into bucket (worked great). Then it drove great, no more power loss problem, that is until I added a little more fluid to bring it up to proper height and accidently went overboard, so the problem returned at lower speeds. Tomarrow I'll drain extra out and hope (expect) all to be well. Guess these automatic trannies are sensitive creatures. They like new fluid and they like it at the exact proper level (though I think they run better slightly low on fluid then they do to high).

RE: power loss in phases, 89n MPV 6 cyl auto trans
 

totally fixed by replacing the oxygen sensor unit and changing the transmission fluid. I love this MPV now. Only problem left is a little smoke from the engine compartment and engine running cool. I've just posted two messages regarding this and hoping to hear on that soon.
thanks